Kavon Farvardin authored Oct 28, 2018 and Ben Gamari committed Oct 28, 2018

We now calculate the SSE register padding needed to fix the calling
convention in LLVM in a robust way: grouping them by whether
registers in that class overlap (with the same class overlapping
itself).

My prior patch assumed that no matter the platform, physical
register Fx aliases with Dx, etc, for our calling convention.

This is unfortunately not the case for any platform except x86-64.

Test Plan:
Only know how to test on x86-64, but it should be tested on ARM with:

`make test WAYS=llvm && make test WAYS=optllvm`

Reviewers: bgamari, angerman

Reviewed By: bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #15780, #14251, #15747

Differential Revision: https://phabricator.haskell.org/D5254