kbuild: fix cc-option and cc-option-yn

David Sanders wrote:

> I'm getting this error:
> as: unrecognized option `-mtune=generic32'
> I have binutils 2.17.

Use -c instead of -S in cc-option and cc-option-yn, so we can probe
options related to the assembler.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: kbuild devel <kbuild-devel@lists.sourceforge.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>