`conv-bits-runtime-const` gates `f16` and `f128` tests behind `x86_64`,
but this isn't always accurate. In particular, x86 `MinGW` has an ABI
bug [1] which means things work when linked to our Rust math libraries
but don't work with host libraries. RUST-143405 slightly adjusts which
targets we provide `f16` and `f128` symbols for and effectively removes
MinGW from that list, meaning host libraries start getting linked,
meaning `f16` and `f128` tests start to fail.
Account for this by changing the gates in one such test to
`cfg(target_has_reliable_{f16,f128})` which is the way we should be
gating all behavior related to the types going forward.
`rustfmt` also seems to have formatted the macros which is fine.
[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054
