Add `frexpf16`, `frexpf128`, `ilogbf16`, and `ilogbf128`#862

tgross35 wants to merge 1 commit intorust-lang:mainrust-lang/compiler-builtins:mainfrom

tgross35:generic-frexp-ilogbtgross35/compiler-builtins:generic-frexp-ilogbCopy head branch name to clipboard