Support negative lookahead for tokenizer in ios llama app (pytorch#10592)

Author: jackzhxng

examples/demo-apps/apple_ios/LLaMA/LLaMA.xcodeproj/project.pbxproj

@@ -818,6 +818,7 @@
 					"DEBUG=1",
 					"ET_USE_TIKTOKEN=1",
 				);
+				GCC_PREPROCESSOR_DEFINITIONS = "SUPPORT_REGEX_LOOKAHEAD=ON";
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_KEY_NSHumanReadableCopyright = "";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
@@ -854,6 +855,7 @@
 				ENABLE_MODULE_VERIFIER = YES;
 				GCC_C_LANGUAGE_STANDARD = gnu17;
 				GCC_PREPROCESSOR_DEFINITIONS = "ET_USE_TIKTOKEN=1";
+				GCC_PREPROCESSOR_DEFINITIONS = "SUPPORT_REGEX_LOOKAHEAD=ON";
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_KEY_NSHumanReadableCopyright = "";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";