[libc] Fix x86_64 fenv implementation for windows

All fenv functions are also enabled for windows. Since two tests,
enabled_exceptions_test and feholdexcept_test are still failing on
windows, they have been disabled.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D106808

GitOrigin-RevId: dd8b93a9e76bc5e3c8fc521fcb06c779371211d3
3 files changed