Enable aidl#generate_traces by default for Cpp

Test: Manual
Bug: 161393989
Change-Id: I0bbd42217c85e42b2a739b46bb2177186cfd40ed
diff --git a/cc/compiler.go b/cc/compiler.go
index 3c904b8..f9f7b6f 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -565,7 +565,7 @@
 			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")
 		}