Add support for AUTO_*_INITIALIZE to build/soong.

Bug: http://b/131390872
Test: Builds with/without AUTO_ZERO_INITIALIZE set.
Test: Builds with/without AUTO_PATTERN_INITIALIZE set.

Change-Id: If085ec53c619e2cebc86ca23f7039298160d99ae
diff --git a/cc/config/global.go b/cc/config/global.go
index a27246e..9ce6896 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -150,8 +150,22 @@
 	pctx.StaticVariable("HostGlobalLdflags", strings.Join(hostGlobalLdflags, " "))
 	pctx.StaticVariable("HostGlobalLldflags", strings.Join(hostGlobalLldflags, " "))
 
-	pctx.StaticVariable("CommonClangGlobalCflags",
-		strings.Join(append(ClangFilterUnknownCflags(commonGlobalCflags), "${ClangExtraCflags}"), " "))
+	pctx.VariableFunc("CommonClangGlobalCflags", func(ctx android.PackageVarContext) string {
+		flags := ClangFilterUnknownCflags(commonGlobalCflags)
+		flags = append(flags, "${ClangExtraCflags}")
+
+		// http://b/131390872
+		// Automatically initialize any uninitialized stack variables.
+		// Prefer zero-init if both options are set.
+		if ctx.Config().IsEnvTrue("AUTO_ZERO_INITIALIZE") {
+			flags = append(flags, "-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang")
+		} else if ctx.Config().IsEnvTrue("AUTO_PATTERN_INITIALIZE") {
+			flags = append(flags, "-ftrivial-auto-var-init=pattern")
+		}
+
+		return strings.Join(flags, " ")
+	})
+
 	pctx.VariableFunc("DeviceClangGlobalCflags", func(ctx android.PackageVarContext) string {
 		if ctx.Config().Fuchsia() {
 			return strings.Join(ClangFilterUnknownCflags(deviceGlobalCflags), " ")