This was a bit trickier than it should be due to symbol conflicts with
zig's compiler-rt implementation. We attempt to use weak linkage in
our compiler-rt, but this does not seem to be working in all cases. I
manually disabled export of the problematic compiler-rt math functions
in order to cross compile musl's libc.so for all targets as input to
`tools/gen_stubs.zig`.
Other than that, this update went fairly smoothly. Quite a few
additional symbols were added to the blacklist in `tools/gen_stubs.zig`
due to recent reorganization of zig's compiler-rt.
