This commit adds support for LLVM 16 and switches to it by default. That
means three LLVM versions are supported at the same time: LLVM 14, 15,
and 16.
This commit includes work by QuLogic:
* Part of this work was based on a PR by QuLogic:
https://github.com/tinygo-org/tinygo/pull/3649
But I also had parts of this already implemented in an old branch I
already made for LLVM 16.
* QuLogic also provided a CGo fix here, which is also incorporated in
this commit:
https://github.com/tinygo-org/tinygo/pull/3869
The difference with the original PR by QuLogic is that this commit is
more complete:
* It switches to LLVM 16 by default.
* It updates some things to also make it work with a self-built LLVM.
* It fixes the CGo bug in a slightly different way, and also fixes
another one not included in the original PR.
* It does not keep compiler tests passing on older LLVM versions. I
have found this to be quite burdensome and therefore don't generally
do this - the smoke tests should hopefully catch most regressions.
This makes reviewing PRs a lot easier because I don't have to run this
myself :)
This only uses the drivers repo so far, which is a good starting point
but doesn't include binary size changes for WebAssembly for example. A
future change could add some real-world programs to get a better idea of
the real-world impact.
To be clear: the intention is not to just look at the number at the
bottom. It is important to look at the actual size difference to see the
overall pattern (like, the difference may be due to a few outlier).
