gcc: Specify '--with-headers' when building final gcc

The final gcc build process was relying on `CT_CC_SYSROOT_ARG` to
provide the `--with-headers` argument pointing to the libc header
directory.

Since `CT_CC_SYSROOT_ARG` no longer provides `--with-headers`, this adds
one directly to the final gcc build invocation.

Without this, gcc build system will not copy all the required libc
headers into the `sys-include` directory.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

scripts/build/cc/gcc.sh

@@ -280,6 +280,7 @@ do_gcc_core_backend() {
         gcc_build|gcc_host)
             CT_DoLog EXTRA "Configuring final gcc compiler"
             extra_config+=( "${CT_CC_SYSROOT_ARG[@]}" )
+            extra_config+=( "--with-headers=${CT_PREFIX_DIR}/${CT_TARGET}/include" )
             extra_user_config=( "${CT_CC_GCC_EXTRA_CONFIG_ARRAY[@]}" )
             log_txt="final gcc compiler"
             # to inhibit the libiberty and libgcc tricks later on