[x86] Fix the test case added in r214670 and tweaked in r214674 further.

[x86] Fix the test case added in r214670 and tweaked in r214674 further.

Fundamentally, there isn't a really portable way to test the constant
pool contents. Instead, pin this test to the bare-metal triple. This
also makes it a 64-bit triple which allows us to only match a single
constant pool rather than two. It can also just hard code the '.' prefix
as the format should be stable now that it has a fixed triple. Finally,
I've switched it to use CHECK-NEXT to be more precise in the instruction
sequence expected and to use variables rather than hard coding decisions
by the register allocator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214679 91177308-0d34-0410-b5e6-96231b3b80d8