[x86] NFC: Clean up two tests and generate precise checks for them.

Mostly this involved giving unnamed values names and running the IR
through `opt` to re-format it but merging in any important comments in
the original. I then deleted pointless comments and inlined the function
attributes for ease of reading and editting.

All of this is to make it much easier to see the instructions being
generated here and evaluate any updates to the tests.

llvm-svn: 311634