picolibc: Build libstdc++ against picolibc if requested

This uses the gcc support for building libstdc++ using alternate lib
header files.

Signed-off-by: Keith Packard <keithp@keithp.com>

config/comp_libs/picolibc.in

@@ -10,6 +10,16 @@
 ## help conglomeration of several library parts, all under BSD-compatible software
 ## help licenses that make them easily usable on embedded products.
 
+config LIBC_PICOLIBC_GCC_LIBSTDCXX
+    bool
+    prompt "Compile libstdc++ picolibc variant"
+    default y
+    depends on CC_LANG_CXX
+    help
+      This option compiles an additional target libstdc++ for use with
+      picolibc. This version is linked when "--specs=picolibcpp.specs"
+      is specified.
+
 config LIBC_PICOLIBC_CXA_ATEXIT
     def_bool y
     select LIBC_PROVIDES_CXA_ATEXIT

samples/arm-picolibc-eabi/crosstool.config

@@ -8,3 +8,4 @@ CT_CC_GCC_CONFIG_TLS=y
 CT_TARGET_CFLAGS="-ftls-model=local-exec"
 CT_CC_GCC_MULTILIB_LIST="rmprofile"
 CT_COMP_LIBS_PICOLIBC=y
+CT_CC_LANG_CXX=y

scripts/build/companion_libs/340-picolibc.sh

@@ -22,6 +22,50 @@ do_picolibc_extract() {
     CT_ExtractPatch PICOLIBC
 }
 
+#------------------------------------------------------------------------------
+# Build an additional target libstdc++ with "-Os" (optimise for speed) option
+# flag for libstdc++ "picolibc" variant.
+do_cc_libstdcxx_picolibc()
+{
+    local -a final_opts
+    local final_backend
+
+    if [ "${CT_LIBC_PICOLIBC_GCC_LIBSTDCXX}" = "y" ]; then
+        final_opts+=( "host=${CT_HOST}" )
+	final_opts+=( "libstdcxx_name=picolibc" )
+        final_opts+=( "prefix=${CT_PREFIX_DIR}" )
+        final_opts+=( "complibs=${CT_HOST_COMPLIBS_DIR}" )
+        final_opts+=( "cflags=${CT_CFLAGS_FOR_HOST}" )
+        final_opts+=( "ldflags=${CT_LDFLAGS_FOR_HOST}" )
+        final_opts+=( "lang_list=c,c++" )
+        final_opts+=( "build_step=libstdcxx" )
+	final_opts+=( "extra_config+=('--enable-stdio=stdio_pure')" )
+	if [ "${CT_LIBC_PICOLIBC_ENABLE_TARGET_OPTSPACE}" = "y" ]; then
+	    final_opts+=( "enable_optspace=yes" )
+	fi
+
+        if [ "${CT_BARE_METAL}" = "y" ]; then
+            final_opts+=( "mode=baremetal" )
+            final_opts+=( "build_libgcc=yes" )
+            final_opts+=( "build_libstdcxx=yes" )
+            final_opts+=( "build_libgfortran=yes" )
+            if [ "${CT_STATIC_TOOLCHAIN}" = "y" ]; then
+                final_opts+=( "build_staticlinked=yes" )
+            fi
+            final_backend=do_gcc_core_backend
+        else
+            final_backend=do_gcc_backend
+        fi
+
+        CT_DoStep INFO "Installing libstdc++ picolibc"
+        CT_mkdir_pushd "${CT_BUILD_DIR}/build-cc-libstdcxx-picolibc"
+        "${final_backend}" "${final_opts[@]}"
+        CT_Popd
+
+        CT_EndStep
+    fi
+}
+
 do_picolibc_for_target() {
     local -a picolibc_opts
     local cflags_for_target
@@ -119,6 +163,8 @@ EOF
 
     CT_Popd
     CT_EndStep
+
+    do_cc_libstdcxx_picolibc
 }
 
 fi