[test] Re-enable accidentally disabled X86 tests

A number of X86 tests were accidentally disabled in
https://reviews.llvm.org/D73568. This commit re-enables those tests.

```
$ for x86_test in $(gg 'REQUIRES: x86$' llvm/test | fst); do sed -i "" '/REQUIRES: x86/d' $x86_test; done
```

(Note that 'x86' is not an available feature, that's what caused the
tests to be disabled.)