Attempt to appease msc buildbot

Attempt to appease msc buildbot

It was timing out on this test, but for reasons unrelated to the
specific bug it was testing for. Randomly breaking in gdb with `clang
-target i686-windows -fmsc-version=1700` reveals *many* frames from
MicrosoftCXXNameMangler. So, it would seem that some caching is needed
there, as well...

Fingers crossed that specifying a triple is sufficient to work around
this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@310444 91177308-0d34-0410-b5e6-96231b3b80d8