Extract out Visibility flags

Bug: 261733820
Test: Unit tests
Change-Id: Ief4ca3b34de6df9a613e94fd31b447a7bb1f04f8

cc/config/global.go

@@ -321,6 +321,9 @@ var (
 	}
 
 	VersionScriptFlagPrefix = "-Wl,--version-script,"
+
+	VisibilityHiddenFlag  = "-fvisibility=hidden"
+	VisibilityDefaultFlag = "-fvisibility=default"
 )
 
 // BazelCcToolchainVars generates bzl file content containing variables for
@@ -411,6 +414,9 @@ func init() {
 
 	exportedVars.ExportString("VersionScriptFlagPrefix", VersionScriptFlagPrefix)
 
+	exportedVars.ExportString("VisibilityHiddenFlag", VisibilityHiddenFlag)
+	exportedVars.ExportString("VisibilityDefaultFlag", VisibilityDefaultFlag)
+
 	// Everything in these lists is a crime against abstraction and dependency tracking.
 	// Do not add anything to this list.
 	commonGlobalIncludes := []string{