[x86] regenerate checks and adjust tests
2 of these tests were clearly not doing what the comments
said they were doing.
The last test was added at rL177933 with no assertions
(presumably it used to crash). But either we don't have
that problem anymore, or this test is folded sooner,
so we don't hit the bug that was fixed by disabling late
FP constant creation. Looking at this as part of reviewing