libc/newlib: Add extra config for newlib.

So users can input config like --enable-newlib-register-fini.

Reviewed-by: Michael Hope
Signed-off-by: Zhenqiang Chen <zhenqiang.chen@linaro.org>

config/libc/newlib.in.2

@@ -35,3 +35,9 @@ config LIBC_NEWLIB_DISABLE_SUPPLIED_SYSCALLS
 	  _write... If you plan to port newlib to a new
 	  platform/board, say Yes.
 
+config LIBC_NEWLIB_EXTRA_CONFIG_ARRAY
+    string
+    prompt "Extra config for newlib"
+    default ""
+    help
+      Extra flags to pass onto ./configure when configuring the newlib.

scripts/build/libc/newlib.sh

@@ -99,7 +99,8 @@ do_libc_start_files() {
         --host=${CT_BUILD}                              \
         --target=${CT_TARGET}                           \
         --prefix=${CT_PREFIX_DIR}                       \
-        "${newlib_opts[@]}"
+        "${newlib_opts[@]}"                             \
+        "${CT_LIBC_NEWLIB_EXTRA_CONFIG_ARRAY[@]}"
 
     CT_DoLog EXTRA "Building C library"
     CT_DoExecLog ALL make ${JOBSFLAGS}