Summary:
Some implementations of fenv.h use macros to define the functions they provide. This can cause problems when `std::fegetround()` is spelled in source.
This patch adds a `fenv.h` header to libc++ for the sole purpose of turning those macros into real functions.
Reviewers: rsmith, mclow.lists, ldionne
Reviewed By: rsmith
Subscribers: mgorny, christof, libcxx-commits
Differential Revision: https://reviews.llvm.org/D57729
llvm-svn: 353767
cf39dd44b8