Add `powi` fo `f16` and `f128` This will unblock adding support to compiler_builtins (<https://github.com/rust-lang/compiler-builtins/pull/614>), which will then unblock adding tests for these new functions.
Add `powi` fo `f16` and `f128` This will unblock adding support to compiler_builtins (<https://github.com/rust-lang/compiler-builtins/pull/614>), which will then unblock adding tests for these new functions.