msun/riscv: expose fe{disable,enable}except

[brooks]

Summary

This is required for GCC to build. Play the Tier-2 card and don't care
about ABI disruption on soft-float, especially since we don't provide
such a target arch any more.

PR: 272759
Reported by: [e-mail]
Submitted by: jrtc27

[jrtc27]

By ABI break you mean for riscv64sf getting the old symbol versions? That architecture is dead, we should just delete the dead code in the header.

[brooks]

In D44333#1011114, @jrtc27 wrote:

By ABI break you mean for riscv64sf getting the old symbol versions? That architecture is dead, we should just delete the dead code in the header.

OK, I'll do that is a separate commit.