[X86] Update the fp128/i128 test to show stack alignment (NFC) (#148753)

Adding an extra argument before a `fp128` only changes the stack offset
by four bytes, while it should instead go in the next 16-aligned slot.
Add a test demonstrating the current behavior.

`no_x86_scrub_sp` is added because offset from the stack pointer is
needed to show the problem.

Relevant issue: #77401

Author: tgross35