Verifier: Call verifyModule() from llc and opt

Change `llc` and `opt` to run `verifyModule()`.  This ensures that we
check the full module before `FunctionPass::doInitialization()` ever
gets called (I was getting crashes in `DwarfDebug` instead of verifier
failures when testing a WIP patch that checks operands of compile
units).  In `opt`, also move up debug-info-stripping so that it still
runs before verification.

There was a fair bit of broken code that was sitting in tree.
Interestingly, some were cases of a `select` that referred to itself in
`-instcombine` tests (apparently an intermediate result).  I split them
off to `*-noverify.ll` tests with RUN lines like this:

    opt < %s -S -disable-verify -instcombine | opt -S | FileCheck %s

This avoids verifying the input file (so we can get the broken code into
`-instcombine), but still verifies the output with a second call to
`opt` (to verify that `-instcombine` will clean it up like it should).

llvm-svn: 233432