Expose Soong's default clang versions to Bazel

As `CLANG_DEFAULT_*VERSION` static strings

Bug: 192058388
Test: Existing tests pass
Change-Id: I047bc3ad9626bf67c12a0b0ac76943c79fb1b4b0
diff --git a/cc/config/global.go b/cc/config/global.go
index 248822f..9773345 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -355,6 +355,9 @@
 	exportedStringListVars.Set("CommonGlobalIncludes", commonGlobalIncludes)
 	pctx.PrefixedExistentPathsForSourcesVariable("CommonGlobalIncludes", "-I", commonGlobalIncludes)
 
+	exportStringStaticVariable("CLANG_DEFAULT_VERSION", ClangDefaultVersion)
+	exportStringStaticVariable("CLANG_DEFAULT_SHORT_VERSION", ClangDefaultShortVersion)
+
 	pctx.SourcePathVariable("ClangDefaultBase", ClangDefaultBase)
 	pctx.VariableFunc("ClangBase", func(ctx android.PackageVarContext) string {
 		if override := ctx.Config().Getenv("LLVM_PREBUILTS_BASE"); override != "" {