Avoid re-entrancy between __sanitizer::Report, OutputDebugString, and RtlRaiseException

Our Report implementation calls OutputDebugString, which calls
RtlRaiseException, which can re-enter back into the ASan runtime and
cause a hang.

Don't treat this special debugger-only exception code as a noreturn
event, since the stack won't really unwind all the way.

llvm-svn: 277763