Fixing compiler issue due to vaargs issues in Xcode compiler.

expect.xcodeproj/project.pbxproj

@@ -196,6 +196,7 @@
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
+				WARNING_CFLAGS = "-Wno-gnu-zero-variadic-macro-arguments";
 			};
 			name = Debug;
 		};
@@ -232,6 +233,7 @@
 				MACOSX_DEPLOYMENT_TARGET = 10.10;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = macosx;
+				WARNING_CFLAGS = "-Wno-gnu-zero-variadic-macro-arguments";
 			};
 			name = Release;
 		};