feat: include a version string from git at build time

[wbruna]

A simple POC for adding a version string to the library and main.cpp (#1005).

The CMake logic comes directly from ggml/CMakeLists.txt. I opted for adding a define to a specific existing source file to make the library easier to build without CMake.

For this test, I added two version strings: a simple commit hash, and a fancier one including the current tag (or last tag and hash if HEAD is not on a tag), and a '+' to indicate file changes:

./sd -v | head -n2
error: the following arguments are required: prompt
stable-diffusion.cpp version master-377-2034588+, commit 2034588
Usage: ./b_w_vulkan/bin/sd [options]

After this commit:

./b_w_vulkan/bin/sd -v | head -n2
error: the following arguments are required: prompt
stable-diffusion.cpp version master-377-2034588-1-gff8abbf, commit ff8abbf
Usage: ./b_w_vulkan/bin/sd [options]

[wbruna]

I'm grabbing the -v like this just to make it easier to test, since parse_args aborts the program on error.