Enable aidl#generate_traces by default for Cpp

Test: Manual
Bug: 161393989
Change-Id: I0bbd42217c85e42b2a739b46bb2177186cfd40ed

cc/compiler.go

@@ -565,7 +565,7 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags, deps
 			flags.aidlFlags = append(flags.aidlFlags, includeDirsToFlags(rootAidlIncludeDirs))
 		}
 
-		if Bool(compiler.Properties.Aidl.Generate_traces) {
+		if proptools.BoolDefault(compiler.Properties.Aidl.Generate_traces, true) {
 			flags.aidlFlags = append(flags.aidlFlags, "-t")
 		}