Metal support.

[Priva28]

This PR updates whisper.cpp and adds metal support.

This PR should not be merged to master, however I'm opening it regardless since it provides an example others might find useful in getting whisper.cpp working on Metal. In my experience, combining the WHISPER_USE_COREML and GGML_USE_METAL flags results in a significant performance improvement.

How it works

It relies heavily on symlinks to ensure the correct files are compiled with the correct flags. It was necessary to create two targets:

• whisper_cpp
• whisper_cpp_metal

This is because ggml-metal.m must be compiled with the -fno-objc-arc flag, but whisper-encoder-impl.m will not compile with this flag.

Therefore:

• whisper_cpp has a symlink to ../whisper_cpp_metal/ggml-metal.h
• whisper_cpp_metal has symlinks to ggml header files required by ggml-metal.m as well as the whisper.h overall header file.

Issues

Because of the way SPM works, it isn't capable of including the ggml-metal.metal file as a resource that can be easily accessed and therefore still requires you to manually include it in your Xcode project in the "Copy Files" Build Phase. If anyone can find a way to get this working automatically, please contribute or let me know!

You can get the metal file from here.

Another reason this would probably have to retain in PR state or another branch at least is that SPM has no way of dynamically defining what cSettings flags should be used. Ideally the user of the package would be able to somehow define that they want to use Metal, and only if they do should the DGGML_USE_METAL flag be added.

For now though, this is here for anyone that wants to play around with it.