Sample script that shows the warning for which I want to find the 'foo' to pass to -Werror=foo (same as you'd pass to -Wfoo)

gistfile1.m

#import <Foundation/Foundation.h>

@interface MyClass : NSObject

@end

@implementation MyClass

@end

int main(int argc, char *argv[]) {
	@autoreleasepool {
		MyClass*	theObj = [[MyClass alloc] initWithNum: [NSNumber numberWithInt: 15]];
	}
}

/*
Untitled.m:13:21: warning: instance method '-initWithNum:' not found (return type defaults to 'id')
                MyClass*        theObj = [[MyClass alloc] initWithNum: [NSNumber numberWithInt: 15]];
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.
2012-11-09 14:36:25.887 Untitled[41490:707] -[MyClass initWithNum:]: unrecognized selector sent to instance 0x7ff801c08020
2012-11-09 14:36:25.890 Untitled[41490:707] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MyClass initWithNum:]: unrecognized selector sent to instance 0x7ff801c08020'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff9827a0a6 __exceptionPreprocess + 198
	1   libobjc.A.dylib                     0x00007fff9068e3f0 objc_exception_throw + 43
	2   CoreFoundation                      0x00007fff983106ea -[NSObject(NSObject) doesNotRecognizeSelector:] + 186
	3   CoreFoundation                      0x00007fff982685ce ___forwarding___ + 414
	4   CoreFoundation                      0x00007fff982683b8 _CF_forwarding_prep_0 + 232
	5   Untitled                            0x000000010aad3eea main + 106
	6   libdyld.dylib                       0x00007fff928ed7e1 start + 0
	7   ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminate called throwing an exception
Run Command: line 1: 41490 Abort trap: 6           ./"$2" "${@:3}"
*/