Deprecating clang Property

Clang has defaulted to true since 2018. Clang property is deprecated.
Set up a BUILD_BROKEN_CLANG_PROPERTY flag so partners can bypass \
errors from using clang.

Bug: 208980553
Test: m nothing & treehugger
Change-Id: I8fd7d3e6bdbb963279248d3482e8a590238727e3
diff --git a/android/config.go b/android/config.go
index 5ca9420..6654b49 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1630,6 +1630,10 @@
 	return uncheckedFinalApiLevel(apiLevel)
 }
 
+func (c *deviceConfig) BuildBrokenClangProperty() bool {
+	return c.config.productVariables.BuildBrokenClangProperty
+}
+
 func (c *deviceConfig) BuildBrokenEnforceSyspropOwner() bool {
 	return c.config.productVariables.BuildBrokenEnforceSyspropOwner
 }