Just save XMM0-XMM15 on x64 + more headless

Not really sure why but seems like VS2010 expects XMM4 to be preserved.

Fixes headless on x64.

When the accuracy is there, I figure I might as well, but changing to floats didn't help either.  I found out that timeout was infinity before `PSP_RunLoopFor()`, and 0.0 afterward.  Even if I set it to 86400.0f or anything, it became 0.  Saving XMM4 fixes that.

Anyway, also got the headless auto compare basically feature complete.  Now I just have to make test.py pass the lists of tests to it and nothing else, so it doesn't have to slow down the whole process.  I think it's all the threading and subprocess stuff that is not efficient or something.

-[Unknown]