Merge "Support compiling libgui against musl" am: a98ef807a6

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/1927604

Change-Id: Iee0712f7e646a5d7c56da3f0687274c9169e8806
diff --git a/libs/gui/include/gui/TraceUtils.h b/libs/gui/include/gui/TraceUtils.h
index b9ec14a..e5d2684 100644
--- a/libs/gui/include/gui/TraceUtils.h
+++ b/libs/gui/include/gui/TraceUtils.h
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <stdarg.h>
+
 #include <cutils/trace.h>
 #include <utils/Trace.h>