kconfig: add CC_IS_CLANG and CLANG_VERSION

This will be useful to describe the clang version dependency.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

init/Kconfig

@@ -16,6 +16,13 @@ config GCC_VERSION
 	default $(shell,$(srctree)/scripts/gcc-version.sh -p $(CC) | sed 's/^0*//') if CC_IS_GCC
 	default 0
 
+config CC_IS_CLANG
+	def_bool $(success,$(CC) --version | head -n 1 | grep -q clang)
+
+config CLANG_VERSION
+	int
+	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
+
 config CONSTRUCTORS
 	bool
 	depends on !UML