sudo apt-get install gnustep gnustep-devel gobjc

File .m:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
        NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

        NSLog (@"hello world");
        [pool drain];
        return 0;
}

gcc `gnustep-config --objc-flags` -o hello hello.m -lobjc -lgnustep-base