Current Espressif porting requires standard include as
part of hal implementation. compiler_flags.cmake checks for
variant name to keep those stdinc in build.
Instead of using variant name as check, use this new CONFIG
to make it clear and to allow having toolchain integrated
in zephyr-sdk package.
stdinc dependency in hal_espressif will be worked out and removed
soon.
Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>
c9f6d18dfc