This is a big change: apart from removing LLVM 14 it also removes typed
pointer support (which was only fully supported in LLVM up to version
14). This removes about 200 lines of code, but more importantly removes
a ton of special cases for LLVM 14.
ThinLTO results in a small code size reduction, which is nice
(especially on these very small chips). It also brings us one step
closer to using ThinLTO everywhere.
This commit makes a number of changes:
* It avoids a dependency on Compiler.emitStartGoroutine.
* It moves the func-lowering pass to the transform package.
* It adds testing to func lowering.
No functionality should have changed with this commit.
This code is required by transformation passes which are being moved
into a separate package, but is too complicated to simply copy.
Therefore, I decided to move them into a new package.
