diff --git a/patches/gcc/5.3.0/370-gcc-plugin-Win-Dont-need-undefined-extern-var-refs-nor-fpic.patch b/patches/gcc/5.3.0/370-gcc-plugin-Win-Dont-need-undefined-extern-var-refs-nor-fpic.patch
new file mode 100644
index 00000000..d8986d5f
--- /dev/null
+++ b/patches/gcc/5.3.0/370-gcc-plugin-Win-Dont-need-undefined-extern-var-refs-nor-fpic.patch
@@ -0,0 +1,160 @@
+diff -urN gcc-5.3.0.orig/config/gcc-plugin.m4 gcc-5.3.0/config/gcc-plugin.m4
+--- gcc-5.3.0.orig/config/gcc-plugin.m4	2015-12-19 14:39:04.120734900 +0000
++++ gcc-5.3.0/config/gcc-plugin.m4	2015-12-20 01:28:45.381965300 +0000
+@@ -20,6 +20,9 @@
+ 
+    pluginlibs=
+ 
++   PICFLAG="-fPIC"
++   UNDEFINEDPREAMBLE="extern int X;"
++   UNDEFINEDCODE="return X == 0;"
+    case "${host}" in
+      *-*-darwin*)
+        if test x$build = x$host; then
+@@ -30,6 +33,11 @@
+ 	 export_sym_check=
+        fi
+      ;;
++     *-*-mingw*|*-*-cygwin*|*-*-msys*)
++       PICFLAG=""
++       UNDEFINEDPREAMBLE=""
++       UNDEFINEDCODE=""
++     ;;
+      *)
+        if test x$build = x$host; then
+ 	 export_sym_check="objdump${exeext} -T"
+@@ -81,17 +89,17 @@
+      case "${host}" in
+        *-*-darwin*)
+ 	 CFLAGS=`echo $CFLAGS | sed s/-mdynamic-no-pic//g`
+-	 CFLAGS="$CFLAGS -fPIC"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
+ 	 LDFLAGS="$LDFLAGS -shared -undefined dynamic_lookup"
+        ;;
+        *)
+-	 CFLAGS="$CFLAGS -fPIC"
+-	 LDFLAGS="$LDFLAGS -fPIC -shared"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
++	 LDFLAGS="$LDFLAGS ${PICFLAG} -shared"
+        ;;
+      esac
+-     AC_MSG_CHECKING([for -fPIC -shared])
++     AC_MSG_CHECKING([for ${PICFLAG} -shared])
+      AC_TRY_LINK(
+-       [extern int X;],[return X == 0;],
++       [${UNDEFINEDPREAMBLE}],[${UNDEFINEDCODE}],
+        [AC_MSG_RESULT([yes]); have_pic_shared=yes],
+        [AC_MSG_RESULT([no]); have_pic_shared=no])
+      if test x"$have_pic_shared" != x"yes" -o x"$ac_cv_search_dlopen" = x"no"; then
+diff -urN gcc-5.3.0.orig/gcc/configure gcc-5.3.0/gcc/configure
+--- gcc-5.3.0.orig/gcc/configure	2015-12-19 14:40:16.893975900 +0000
++++ gcc-5.3.0/gcc/configure	2015-12-20 01:28:45.472476700 +0000
+@@ -28386,6 +28386,9 @@
+ 
+    pluginlibs=
+ 
++   PICFLAG="-fPIC"
++   UNDEFINEDPREAMBLE="extern int X;"
++   UNDEFINEDCODE="return X == 0;"
+    case "${host}" in
+      *-*-darwin*)
+        if test x$build = x$host; then
+@@ -28396,6 +28399,11 @@
+ 	 export_sym_check=
+        fi
+      ;;
++     *-*-mingw*|*-*-cygwin*|*-*-msys*)
++       PICFLAG=""
++       UNDEFINEDPREAMBLE=""
++       UNDEFINEDCODE=""
++     ;;
+      *)
+        if test x$build = x$host; then
+ 	 export_sym_check="objdump${exeext} -T"
+@@ -28508,23 +28516,23 @@
+      case "${host}" in
+        *-*-darwin*)
+ 	 CFLAGS=`echo $CFLAGS | sed s/-mdynamic-no-pic//g`
+-	 CFLAGS="$CFLAGS -fPIC"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
+ 	 LDFLAGS="$LDFLAGS -shared -undefined dynamic_lookup"
+        ;;
+        *)
+-	 CFLAGS="$CFLAGS -fPIC"
+-	 LDFLAGS="$LDFLAGS -fPIC -shared"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
++	 LDFLAGS="$LDFLAGS ${PICFLAG} -shared"
+        ;;
+      esac
+-     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for -fPIC -shared" >&5
+-$as_echo_n "checking for -fPIC -shared... " >&6; }
++     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${PICFLAG} -shared" >&5
++$as_echo_n "checking for ${PICFLAG} -shared... " >&6; }
+      cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
+-extern int X;
++${UNDEFINEDPREAMBLE}
+ int
+ main ()
+ {
+-return X == 0;
++${UNDEFINEDCODE}
+   ;
+   return 0;
+ }
+diff -urN gcc-5.3.0.orig/libcc1/configure gcc-5.3.0/libcc1/configure
+--- gcc-5.3.0.orig/libcc1/configure	2015-12-19 14:40:20.855979000 +0000
++++ gcc-5.3.0/libcc1/configure	2015-12-20 01:28:45.504980900 +0000
+@@ -14500,6 +14500,9 @@
+ 
+    pluginlibs=
+ 
++   PICFLAG="-fPIC"
++   UNDEFINEDPREAMBLE="extern int X;"
++   UNDEFINEDCODE="return X == 0;"
+    case "${host}" in
+      *-*-darwin*)
+        if test x$build = x$host; then
+@@ -14510,6 +14513,11 @@
+ 	 export_sym_check=
+        fi
+      ;;
++     *-*-mingw*|*-*-cygwin*|*-*-msys*)
++       PICFLAG=""
++       UNDEFINEDPREAMBLE=""
++       UNDEFINEDCODE=""
++     ;;
+      *)
+        if test x$build = x$host; then
+ 	 export_sym_check="objdump${exeext} -T"
+@@ -14622,23 +14630,23 @@
+      case "${host}" in
+        *-*-darwin*)
+ 	 CFLAGS=`echo $CFLAGS | sed s/-mdynamic-no-pic//g`
+-	 CFLAGS="$CFLAGS -fPIC"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
+ 	 LDFLAGS="$LDFLAGS -shared -undefined dynamic_lookup"
+        ;;
+        *)
+-	 CFLAGS="$CFLAGS -fPIC"
+-	 LDFLAGS="$LDFLAGS -fPIC -shared"
++	 CFLAGS="$CFLAGS ${PICFLAG}"
++	 LDFLAGS="$LDFLAGS ${PICFLAG} -shared"
+        ;;
+      esac
+-     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for -fPIC -shared" >&5
+-$as_echo_n "checking for -fPIC -shared... " >&6; }
++     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${PICFLAG} -shared" >&5
++$as_echo_n "checking for ${PICFLAG} -shared... " >&6; }
+      cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
+-extern int X;
++${UNDEFINEDPREAMBLE}
+ int
+ main ()
+ {
+-return X == 0;
++${UNDEFINEDCODE}
+   ;
+   return 0;
+ }
diff --git a/patches/gcc/5.3.0/380-gcc-plugin-POSIX-include-sys-select-h.patch b/patches/gcc/5.3.0/380-gcc-plugin-POSIX-include-sys-select-h.patch
new file mode 100644
index 00000000..12ef48ee
--- /dev/null
+++ b/patches/gcc/5.3.0/380-gcc-plugin-POSIX-include-sys-select-h.patch
@@ -0,0 +1,11 @@
+diff -urN gcc-5.3.0.orig/libcc1/connection.cc gcc-5.3.0/libcc1/connection.cc
+--- gcc-5.3.0.orig/libcc1/connection.cc	2015-12-19 14:40:20.860479600 +0000
++++ gcc-5.3.0/libcc1/connection.cc	2015-12-20 01:31:04.346611500 +0000
+@@ -21,6 +21,7 @@
+ #include <string>
+ #include <unistd.h>
+ #include <sys/types.h>
++#include <sys/select.h>
+ #include <string.h>
+ #include <errno.h>
+ #include "marshall.hh"
diff --git a/scripts/build/companion_libs/200-libelf.sh b/scripts/build/companion_libs/200-libelf.sh
index 58aa3155..529bba22 100644
--- a/scripts/build/companion_libs/200-libelf.sh
+++ b/scripts/build/companion_libs/200-libelf.sh
@@ -135,6 +135,13 @@ do_libelf_backend() {
     CT_DoExecLog ALL ${make}
 
     CT_DoLog EXTRA "Installing libelf"
+
+    # Guard against $destdir$prefix == //
+    # which is a UNC path on Cygwin/MSYS2
+    if [[ ${destdir} == / ]] && [[ ${prefix} == /* ]]; then
+        destdir=
+    fi
+
     CT_DoExecLog ALL ${make} instroot="${destdir}" install
 }
 
diff --git a/scripts/build/companion_libs/210-expat.sh b/scripts/build/companion_libs/210-expat.sh
old mode 100644
new mode 100755
index 304482cd..7801d339
--- a/scripts/build/companion_libs/210-expat.sh
+++ b/scripts/build/companion_libs/210-expat.sh
@@ -22,13 +22,18 @@ if [ "${CT_EXPAT}" = "y" ]; then
 # Do not need expat for build at this time.
 
 do_expat_for_host() {
+    local -a expat_opts
+
     CT_DoStep INFO "Installing expat for host"
     CT_mkdir_pushd "${CT_BUILD_DIR}/build-expat-host-${CT_HOST}"
 
-    do_expat_backend host="${CT_HOST}" \
-                     prefix="${CT_HOST_COMPLIBS_DIR}" \
-                     cflags="${CT_CFLAGS_FOR_HOST}" \
-                     ldflags="${CT_LDFLAGS_FOR_HOST}"
+    expat_opts+=( "host=${CT_HOST}" )
+    expat_opts+=( "prefix=${CT_HOST_COMPLIBS_DIR}" )
+    expat_opts+=( "cflags=${CT_CFLAGS_FOR_HOST}" )
+    expat_opts+=( "ldflags=${CT_LDFLAGS_FOR_HOST}" )
+    expat_opts+=( "static_build=${CT_STATIC_TOOLCHAIN}" )
+
+    do_expat_backend "${expat_opts[@]}"
 
     CT_Popd
     CT_EndStep
@@ -37,12 +42,17 @@ fi
 
 if [ "${CT_EXPAT_TARGET}" = "y" ]; then
 do_expat_for_target() {
+    local -a expat_opts
+
     CT_DoStep INFO "Installing expat for target"
     CT_mkdir_pushd "${CT_BUILD_DIR}/build-expat-target-${CT_TARGET}"
 
-    do_expat_backend host="${CT_TARGET}" \
-                     prefix="/usr" \
-                     destdir="${CT_SYSROOT_DIR}"
+    expat_opts+=( "host=${CT_TARGET}" )
+    expat_opts+=( "prefix=/usr" )
+    expat_opts+=( "destdir=${CT_SYSROOT_DIR}" )
+    expat_opts+=( "static_build=y" )
+
+    do_expat_backend "${expat_opts[@]}"
 
     CT_Popd
     CT_EndStep
@@ -60,11 +70,17 @@ do_expat_backend() {
     local cflags
     local ldflags
     local arg
+    local -a extra_config
 
     for arg in "$@"; do
         eval "${arg// /\\ }"
     done
 
+    if [ "${static_build}" = "y" ]; then
+        extra_config+=("--disable-shared")
+        extra_config+=("--enable-static")
+    fi
+
     CT_DoLog EXTRA "Configuring expat"
 
     CT_DoExecLog CFG                                                \
@@ -74,8 +90,7 @@ do_expat_backend() {
         --build=${CT_BUILD}                                         \
         --host=${host}                                              \
         --prefix="${prefix}"                                        \
-        --enable-static                                             \
-        --disable-shared
+        "${extra_config[@]}"
 
     CT_DoLog EXTRA "Building expat"
     CT_DoExecLog ALL ${make} ${JOBSFLAGS}
diff --git a/scripts/build/companion_libs/320-libiconv.sh b/scripts/build/companion_libs/320-libiconv.sh
index 06908b54..0c9e5cf6 100644
--- a/scripts/build/companion_libs/320-libiconv.sh
+++ b/scripts/build/companion_libs/320-libiconv.sh
@@ -102,6 +102,7 @@ do_libiconv_backend() {
         --build=${CT_BUILD}                                   \
         --host="${host}"                                      \
         --prefix="${prefix}"                                  \
+        --disable-nls                                         \
         "${extra_config[@]}"                                  \
 
     CT_DoLog EXTRA "Building libiconv"