This reverts commit 87cef78fa1.
The issue in the original revert is that a lit test expecting a `-nan`
as an output was failing on M2. Since the IEEE 754-2008 standard does
not require the sign to be printed when displaying a `nan`, this
commit changes the `CHECK` for `-nan` to one that checks the result
value bitcasted to an `i32` to ensure that input is being left
unchanged. This check should now be independent of platform being used
to run test.
Reviewed By: jpienaar, mehdi_amini
Differential Revision: https://reviews.llvm.org/D148941