Add proto property struct

The ProtoProperties struct was not being added to the property struct
list, preventing proto.type and proto.static properties from being set
in Android.bp files.

Bug: 32286026
Test: Add proto.type to system/extras/perfprofd/Android.bp, run soong
Change-Id: I9a5b63ddd3e7a53881ddbfd381c42aa1b4c4f454

cc/compiler.go

@@ -115,7 +115,7 @@ func (compiler *baseCompiler) appendAsflags(flags []string) {
 }
 
 func (compiler *baseCompiler) compilerProps() []interface{} {
-	return []interface{}{&compiler.Properties}
+	return []interface{}{&compiler.Properties, &compiler.Proto}
 }
 
 func (compiler *baseCompiler) compilerInit(ctx BaseModuleContext) {}