Automatically integrate generated C code into Haskell code

[wavewave]

It would be very convenient if auto-generated C code is automatically embedded into Haskell modules and ready for the use as FFI function on user's side.
This is possible in Template Haskell using https://hackage.haskell.org/package/template-haskell-2.18.0.0/docs/Language-Haskell-TH-Syntax.html#v:addForeignSource (this is how inline-c works)
Let's discuss about whether and how to support such utility functions.

[wavewave]

This is a snippet showing how to use that generated C code integration.
https://github.com/wavewave/ghc-clang/blob/7bbb0c8b3c444bb1c7be7ab1d8b64cb95ff209c9/TH.hs
https://github.com/wavewave/ghc-clang/blob/7bbb0c8b3c444bb1c7be7ab1d8b64cb95ff209c9/test.hs
Note that in that experiment, I set up GHC with clang only.

[wavewave]

By the way, we have withJitFunction, so still need to weigh the benefit of tighter integration into GHC pipeline through addForeignSource compared with that approach.

[wavewave]

internally, withJitFunction uses shared object dynamic loading mechanism on the fly. Potentially, this can be complicated in various environment compared with statically linking generated C code via addForeignSource. In the end, template haskell approach (a la inline-c) is simpler prospectively.

[wavewave]

experimented #69 and now created an issue #71
I will work on this for some time.