kasan: Makefile: shut up warnings if CONFIG_COMPILE_TEST=y

It might be annoying to constantly see this:

	scripts/Makefile.kasan:16: Cannot use CONFIG_KASAN: -fsanitize=kernel-address is not supported by compiler

while performing allmodconfig/allyesconfig build tests.
Disable this warning if CONFIG_COMPILE_TEST=y.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 6e54abac1b8e0b7febffdbad37b605daef1cfcff
Git-repo: https://github.com/torvalds/linux.git


Change-Id: I8ad838226fd9b57262538edd4ebaec6565b64a53
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>