[PATCH] Fix "#pragma clang __debug overflow_stack" for MSVC builds

[Greg Bedwell]

...and right as I hit submit I realised I submitted my non-clang-formatted version, but Phabricator is not letting me submit an updated version at the moment.  d'oh!

obviously should look like this:

void *StackUser = &StackUser;

http://reviews.llvm.org/D5109