[x86] Make some questionable tests not spew assembly to stdout, which
makes a mess of the lit output when they ultimately fail.

The 2012-10-02-DAGCycle test is really frustrating because the *only*
explanation for what it is testing is a rdar link. I would really rather
that rdar links (which are not public or part of the open source
project) were not committed to the source code. Regardless, the actual
problem *must* be described as the rdar link is completely opaque. The
fact that this test didn't check for any particular output further
exacerbates the inability of any other developer to debug failures.

The mem-promote-integers test has nice comments and *seems* to be
a great test for our lowering... except that we don't actually check
that any of the generated code is correct or matches some pattern. We
just avoid crashing. It would be great to go back and populate this test
with the actual expectations.