[x86] Merge the third combining test into the generic one and add proper
checks for all the ISA variants.

If the SSE2 checks here terrify you, good. This is (in large part) the
kind of amazingly bad code that is holding LLVM back when vectorizing on
older ISAs.

At the same time, these tests seem increasingly dubious to me. There are
a very large number of tests and it isn't clear that they are
systematically covering a specific set of functionality. Anyways,
I don't want to reduce testing during the transition, I just want to
consolidate it to where it is easier to manage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218860 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Merge still more combine tests into the common file. These at
least seem *slightly* more interesting test wise, although given how
spotily we actually combine anything, I remain somewhat suspicious.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218861 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Just delete the last combine test file.

This file isn't really doing anything useful. Many of the tests that
seem to be combined are also repeats from other test files. Many of the
other tests, despite the comment that they should be combined into
a single shuffle... well... aren't combined into a single shuffle.
=/

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218862 91177308-0d34-0410-b5e6-96231b3b80d8