Kconfig: Add option to make clang the default compiler

Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Change-Id: Ie910f654abdb8d79c686363d2bd8af4ceeea4087
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76436
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/Kconfig b/src/Kconfig
index ea6f341..1549719 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -47,8 +47,15 @@
 	  Select the prefix to all files put into the image. It's "fallback"
 	  by default, "normal" is a common alternative.
 
+config DEFAULT_COMPILER_LLVM_CLANG
+	bool
+	help
+	  Allows to override the default compiler. This can for instance be
+	  set in site-local/Kconfig.
+
 choice
 	prompt "Compiler to use"
+	default COMPILER_LLVM_CLANG if DEFAULT_COMPILER_LLVM_CLANG
 	default COMPILER_GCC
 	help
 	  This option allows you to select the compiler used for building