Support alternative Objective-C build process

[moreau-nicolas]

The current Objective-C build process uses Xcode, which is not available on Linux. I suggest moving to a more platform-independant alternative, such as gcc-objc.

At the moment a fresh git clone of the project cannot compile on a Linux box (or even a Windows one).

[aslakhellesoy]

Yeah requiring xcode is obviously not ideal. Would you be interested in sending a PR to address this?

[moreau-nicolas]

I'm willing, but I'm not sure I'm the best person to do this: I don't have access to an Apple computer and have no experience at all with Objective-C.

[aslakhellesoy]

Isn't the point of this bug to make the build pass on a non-apple computer (Linux and/or Windows)?

[moreau-nicolas]

Of course it is! My feeling of not-being-the-best-guy-for-the-job is more related to my lack of knowledge on Objective-C than lack of a computer.
I'll try and propose something.

[aslakhellesoy]

I don't know Objective-C either, and I don't think you need to know any in order to compile it ;-)

[moreau-nicolas]

I just tried to (naively) compile all *.m files into object files with gcc 4.8 but it does not work.
Clang 3.4 does not work either.
Both don't seem to support *.pch files, so I tried manually importing <Foundation/Foundation.h> at the very beginning of each *.m file, but no dice, it still is not enough.

I got the following error, which seems pretty obscure to me:

GHTag.m:15:13: error: synthesized property 'location' must either be named the same as a compatible instance variable or must
      explicitly name an instance variable
@synthesize location;
            ^
GHTag.m:16:13: error: synthesized property 'name' must either be named the same as a compatible instance variable or must explicitly
      name an instance variable
@synthesize name;
            ^
2 errors generated.

Here is the command that generated this error:

cd objective-c/Gherkin
clang -ObjC -I/usr/include/GNUstep -c GHTag.m

Maybe @LiohAu could help?