Revert "Revert "Fix handling of special and large vals in expand pattern for...

Revert "Revert "Fix handling of special and large vals in expand pattern for `round`" and "Add pattern that expands `math.roundeven` into `math.round` + arith""

This reverts commit 87cef78f.

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