KMSAN: Restore dynamic check for '-fsanitize=kernel-memory'

Commit 5ff8c11 ("KMSAN: Remove tautological checks") changed
CONFIG_HAVE_KMSAN_COMPILER from a dynamic check for
'-fsanitize=kernel-memory' to just being true for CONFIG_CC_IS_CLANG.
This missed the fact that not all architectures supported
'-fsanitize=kernel-memory' at the same time. For example, SystemZ / s390
gained support for KMSAN in clang-18 [1], so builds with clang-15
through clang-17 can select KMSAN but they error with:

  clang-16: error: unsupported option '-fsanitize=kernel-memory' for target 's390x-unknown-linux-gnu'

Restore the cc-option check for '-fsanitize=kernel-memory' to make sure
the compiler target properly supports '-fsanitize=kernel-memory'. The
check for '-msan-disable-checks=1' does not need to be restored because
all supported clang versions for building the kernel support it.

Fixes: 5ff8c11 ("KMSAN: Remove tautological checks")
Link: llvm/llvm-project@a3e56a8 [1]
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202510220236.AVuXXCYy-lkp@intel.com/
Acked-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/20251023-fix-kmsan-check-s390-clang-v1-1-4e6df477a4cc@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

lib/Kconfig.kmsan

@@ -3,7 +3,7 @@ config HAVE_ARCH_KMSAN
 	bool
 
 config HAVE_KMSAN_COMPILER
-	def_bool CC_IS_CLANG
+	def_bool $(cc-option,-fsanitize=kernel-memory)
 
 config KMSAN
 	bool "KMSAN: detector of uninitialized values use"