Add AUTO_UNINITIALIZE as another option for trivial initialization.

This lets us test uninitialized variables even if we change the defaults
for -ftrivial-auto-var-init.

Bug: 131390872
Test: AUTO_UNINITIALIZE=true m
Change-Id: I2b4473a0547dc9c4d9f081d8af2d283f17f66f7a
diff --git a/cc/config/global.go b/cc/config/global.go
index 87314dc..44de4d5 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -166,6 +166,8 @@
 			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")
+		} else if ctx.Config().IsEnvTrue("AUTO_UNINITIALIZE") {
+			flags = append(flags, "-ftrivial-auto-var-init=uninitialized")
 		}
 
 		return strings.Join(flags, " ")