`cc` automatically reads this from Cargo's `OPT_LEVEL` variable so we
don't need to set it explicitly. Remove this so running in a debugger
makes more sense.
This crate builds math symbols from a musl checkout and provides a Rust
interface. The intent is that we will be able to compare our
implementations against musl on more than just linux (which are the only
currently the only targets we run `*-musl` targets against for
comparison).
Musl libc can't compile on anything other than Linux; however, the
routines in `src/math` are cross platform enough to build on MacOS and
windows-gnu with only minor adjustments. We take advantage of this and
build only needed files using `cc`.
The build script also performs remapping (via defines) so that e.g.
`cos` gets defined as `musl_cos`. This gives us more certainty that we
are actually testing against the intended symbol; without it, it is easy
to unknowingly link to system libraries or even Rust's `libm` itself and
wind up with an ineffective test. There is also a small procedure to
verify remapping worked correctly by checking symbols in object files.
