Rollup merge of #143475 - tgross35:runtime-test-config, r=jieyouxu

tests: Use `cfg_target_has_reliable_f16_f128` in `conv-bits-runtime-const`

`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

Author: tgross35