In running some internal vectorcall tests in 32 bit mode, we discovered that the behavior I'd previously implemented for x64 (and applied to x32) regarding the assignment of SSE registers was incorrect. See spec here: https://msdn.microsoft.com/en-us/library/dn375768.aspx
My previous implementation applied register argument position from the x64 version to both. This isn't correct for x86, so this removes and refactors that section. Additionally, it corrects the integer/int-pointer assignments. Unlike x64, x86 permits integers to be assigned independent of position.
Finally, the code for 32 bit was cleaned up a little to clarify the intent, as well as given a descriptive comment.