* Pass host CPU features to LLVM target
This gets `test_gemm_fp16` to pass on Windows. It would fail because the
generated machine code would call compiler-rt functions to to perform
truncating. This gets the test to pass on some hardware, because LLVM
gets access to more instructions. Essentially this is similar to
`-march=native`.
Unless this was intentionally left as is to be re-implemented fully in
LLVM IR or something.
* Fix linter complaints