The ${STAGING_INCDIR_NATIVE}/gcc-build-internal-$mtarget may not exist
when use the external sdk toolchain, we need check before link for it.
Fixed:
run.do_configure.12538: 149: cd: can't cd to sysroots/x86_64-linux/usr/include/gcc-build-internal-x86_64-wrs-linux
(LOCAL REV: NOT UPSTREAM) -- Sent to oe-core on 20150204
(From OE-Core rev: 82166e514438eb1b562f2a4dc2f9f8fecf3f60df)
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>