Add -fstack-protector back on Mac... turns out it does work on clang.

make-mac.mk

@@ -10,7 +10,7 @@ ifeq ($(ZT_AUTO_UPDATE),1)
 endif
 
 # Uncomment for a release optimized universal binary build
-CFLAGS=-arch i386 -arch x86_64 -Wall -O4 -pthread -mmacosx-version-min=10.6 -DNDEBUG -Wno-unused-private-field $(INCLUDES) $(DEFS)
+CFLAGS=-arch i386 -arch x86_64 -Wall -O4 -fstack-protector -pthread -mmacosx-version-min=10.6 -DNDEBUG -Wno-unused-private-field $(INCLUDES) $(DEFS)
 STRIP=strip
 
 # Uncomment for a debug build