[test] Disable dsymutil update test on windows

Apparently, the issue with dsymutil update functionality on Windows was
that Windows doesn't like dsymutil renaming files that have open handles
to them. This disables the new accelerator test and updates the comment
in the other two test.

We should be able to enable the tests again once we updated the
implementation to use TempFile::keep() to keep the temporary files in
MachOUtils.

A big thank you to Jeremy Morse from Sony for figuring this out and
bringing it to my attention.

llvm-svn: 338030