Prior to doing compiler feature detection in Kconfig, attempts to build
GCC plugins with Clang would fail the build, much in the same way missing
GCC plugin headers would fail the build. However, now that this logic
has been lifted into Kconfig, add an explicit test for GCC (instead of
duplicating it in the feature-test script).
Reported-by: NStefan Agner <stefan@agner.ch>
Signed-off-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

Collect relevant code into the scripts/gcc-plugins directory.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: NKees Cook <keescook@chromium.org>