CMakeLists.txt from contrib/buildsystems fails to build on Mac

[Ilya Kantor <iliakan@gmail.com>]

Hello,

I've just tried to build git as described in contrib/buildsystems/CMakeLists.txt, and it doesn't work.

Is this route supposed to work at all?

I'm on MacOS Ventura,
first running this:
```
mkdir -p contrib/buildsystems/out
cd contrib/buildsystems/out
cmake ../ -DCMAKE_BUILD_TYPE=Release
```

This works fine (the full output is here: https://gist.github.com/11f6786eb195a4bc939e010d4f759a22).

And then I run `make`:

```
make
```

Although it dies with an error.

The full output is here: https://gist.github.com/24e2eb21613668c44d81f6f0cc78e1a1

Here's the ending error:

```
/opt/tmp/git/read-cache.c:170:22: error: no member named 'st_ctim' in 'struct stat'
        sd->sd_ctime.nsec = ST_CTIME_NSEC(*st);
                            ^~~~~~~~~~~~~~~~~~
/opt/tmp/git/contrib/buildsystems/../../git-compat-util.h:1380:48: note: expanded from macro 'ST_CTIME_NSEC'
#define ST_CTIME_NSEC(st) ((unsigned int)((st).st_ctim.tv_nsec))
                                          ~~~~ ^
/opt/tmp/git/read-cache.c:171:22: error: no member named 'st_mtim' in 'struct stat'
        sd->sd_mtime.nsec = ST_MTIME_NSEC(*st);
                            ^~~~~~~~~~~~~~~~~~
/opt/tmp/git/contrib/buildsystems/../../git-compat-util.h:1381:48: note: expanded from macro 'ST_MTIME_NSEC'
#define ST_MTIME_NSEC(st) ((unsigned int)((st).st_mtim.tv_nsec))
                                          ~~~~ ^
/opt/tmp/git/read-cache.c:2410:27: error: no member named 'st_mtim' in 'struct stat'
        istate->timestamp.nsec = ST_MTIME_NSEC(st);
                                 ^~~~~~~~~~~~~~~~~
/opt/tmp/git/contrib/buildsystems/../../git-compat-util.h:1381:48: note: expanded from macro 'ST_MTIME_NSEC'
#define ST_MTIME_NSEC(st) ((unsigned int)((st).st_mtim.tv_nsec))
                                          ~~~~ ^
/opt/tmp/git/read-cache.c:3177:27: error: no member named 'st_mtim' in 'struct stat'
        istate->timestamp.nsec = ST_MTIME_NSEC(st);
                                 ^~~~~~~~~~~~~~~~~
/opt/tmp/git/contrib/buildsystems/../../git-compat-util.h:1381:48: note: expanded from macro 'ST_MTIME_NSEC'
#define ST_MTIME_NSEC(st) ((unsigned int)((st).st_mtim.tv_nsec))
                                          ~~~~ ^
4 errors generated.
make[2]: *** [CMakeFiles/libgit.dir/opt/tmp/git/read-cache.c.o] Error 1
make[1]: *** [CMakeFiles/libgit.dir/all] Error 2
```

May that be because of some changes in MacOs Ventura? 
Or is the CMakeLists.txt "dead and forgotten"? ;)

P.S. The regular "make" route works.

Kind regards,
Ilya Kantor