Suppress unused warnings on YGDefaultLog

Summary:
Suppresses the unused warnings on ```YGDefaultLog```. It uses a more generic macro which simply casts the variable to ```(void)```. This is the simples approach to make mutiple different compilers happy. Fixes #650
Closes #651

Differential Revision: D6407999

Pulled By: emilsjolander

fbshipit-source-id: 19fd78dd8b84eafdbb48875dd003d506a98c4807

yoga/Yoga.cpp

@@ -98,11 +98,15 @@ static int YGAndroidLog(const YGConfigRef config,
   return result;
 }
 #else
+#define YG_UNUSED(x) (void)(x);
+
 static int YGDefaultLog(const YGConfigRef config,
                         const YGNodeRef node,
                         YGLogLevel level,
                         const char *format,
                         va_list args) {
+  YG_UNUSED(config);
+  YG_UNUSED(node);
   switch (level) {
     case YGLogLevelError:
     case YGLogLevelFatal:
@@ -115,6 +119,8 @@ static int YGDefaultLog(const YGConfigRef config,
       return vprintf(format, args);
   }
 }
+
+#undef YG_UNUSED
 #endif
 
 bool YGFloatIsUndefined(const float value) {