Tidy up this rather crufty test. Put the declarations at the top to make

Tidy up this rather crufty test. Put the declarations at the top to make
my C-brain happy. Remove the unnecessary bits of pedantic IR fluff like
nounwind. Remove stray uses comments. Name things semantically rather
than tN so that adding a new test in the middle doesn't cause pain, and
so that new tests can be grouped semantically.

This exposes how little systematic testing is going on here. I noticed
this by finding several bugs via inspection and wondering why this test
wasn't catching any of them. =[

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147248 91177308-0d34-0410-b5e6-96231b3b80d8