fix-tests
[libc] Add extension functions fedisableexcept, feenableexcept and fegetexcept.
[libc] Remove the redundant header FPUtil/FEnvUtils.h
[libc] Add simple x86_64 floating point exception and rounding mode support.
[libc] Add implementations of the remaining fenv functions.
[libc][NFC] Make explicit uint16_t casts in fenv