DEBUG was dropped from the preprocessor macros at some point. Add it...

build/v8.xcodeproj/project.pbxproj

 // !$*UTF8*$!
 {
         archiveVersion = 1;
         classes = {
         };
         objectVersion = 45;
         objects = {
 
 /* Begin PBXAggregateTarget section */
                 7BF891930E73098D000BAF8A /* All */ = {
@@ skipping 1315 matching lines @@
                                 XCODEPROJ_DEPTH = ..;
                         };
                         name = Release;
                 };
                 8970F2F10E719FB2006AE7B5 /* Debug */ = {
                         isa = XCBuildConfiguration;
                         baseConfigurationReference = 7BF891920E73084F000BAF8A /* staticlib.xcconfig */;
                         buildSettings = {
                                 GCC_PREPROCESSOR_DEFINITIONS = (
                                         "$(GCC_PREPROCESSOR_DEFINITIONS)",
+                                        DEBUG,
                                         ENABLE_DISASSEMBLER,
                                         ENABLE_LOGGING_AND_PROFILING,
                                 );
                                 HEADER_SEARCH_PATHS = ../v8/src;
                                 PRODUCT_NAME = v8;
                         };
                         name = Debug;
                 };
                 8970F2F20E719FB2006AE7B5 /* Release */ = {
                         isa = XCBuildConfiguration;
@@ skipping 159 matching lines @@
                                 89F23C930E78D5B6006B2466 /* Debug */,
                                 89F23C940E78D5B6006B2466 /* Release */,
                         );
                         defaultConfigurationIsVisible = 0;
                         defaultConfigurationName = Release;
                 };
 /* End XCConfigurationList section */
         };
         rootObject = 8915B8680E719336009C4E19 /* Project object */;
 }