Hide ARC warnings behind an off-by-default flag.

CMakeLists.txt

@@ -141,6 +141,13 @@ set(OLDABI_COMPAT ${OLD_ABI_COMPAT_DEFAULT} CACHE BOOL
 set(LEGACY_COMPAT FALSE CACHE BOOL
 	"Enable legacy compatibility features")
 
+set(DEBUG_ARC_COMPAT FALSE CACHE BOOL
+	"Log warnings for classes that don't hit ARC fast paths")
+
+if (DEBUG_ARC_COMPAT)
+	add_definitions(-DDEBUG_ARC_COMPAT)
+endif()
+
 if (OLDABI_COMPAT)
 	list(APPEND libobjc_C_SRCS legacy.c abi_version.c statics_loader.c)
 	add_definitions(-DOLDABI_COMPAT=1)

dtable.c

@@ -77,7 +77,6 @@ static BOOL ownsMethod(Class cls, SEL sel)
 }
 
 
-#define DEBUG_ARC_COMPAT
 #ifdef DEBUG_ARC_COMPAT
 #define ARC_DEBUG_LOG(...) fprintf(stderr, __VA_ARGS__)
 #else