Don't declare fenv.h functions when they're a macro.
Don't declare fenv.h functions when they're a macro.

libc still provides function declarations, and these declarations
conflict with libc++'s

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@353774 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx