[x86] Tweak my update script to use test case function names starting

[x86] Tweak my update script to use test case function names starting
with 'stress' to indicate that the specific output isn't interesting and
relax them to only check the last instruction (a ret).

I've updated the one test case that really uses this to name the one
'stress_test' which was actually producing output we can directly check.
With this, the script doesn't introduce noise when run over the v16 test
file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228033 91177308-0d34-0410-b5e6-96231b3b80d8