[Dwarf] Disable reference verification for now (PR32972)

There is no other explanation about why this only started happening
now, even though it crashes on old code (supposedly reachable from
here).

The only common factor between the failing bots is that they use GCC
(4.9 and 5.3) to compile Clang, while the others use Clang 3.8, but the
failure is while building the tests, as an assertion, on Clang.

Commenting it out for now in hope the bots will go back green, but we
should keep looking for the real cause, and update bugzilla.

llvm-svn: 302520