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

back into the V8 Xcode project to make sure that assertions are enabled
in debug builds.

Review URL: http://codereview.chromium.org/21062

git-svn-id: http://src.chromium.org/svn/trunk/src/build@9194 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

v8.xcodeproj/project.pbxproj

@@ -1333,6 +1333,7 @@
 			buildSettings = {
 				GCC_PREPROCESSOR_DEFINITIONS = (
 					"$(GCC_PREPROCESSOR_DEFINITIONS)",
+					DEBUG,
 					ENABLE_DISASSEMBLER,
 					ENABLE_LOGGING_AND_PROFILING,
 				);