Recommit "RunThreadPlan: Fix halting logic in IgnoreBreakpoints = false"

This is a resubmit of r303732, which was reverted due to a regression.

The original patch caused a regression in TestLoadUnload, which has only showed
up when running the remote test suite. The problem there was that we interrupted
the target just as it has hit the rendezvous breakpoint in the dlopen call. This
meant that the stop reason was set to "breakpoint" even though the event would
not have been broadcast if we had not stopped the process. I fix this by
checking StopInfo->ShouldNotify() before stopping.

I also add a new test for the handling of conditional breakpoints in
expressions, which I noticed to be broken (pr33164)

Differential Revision: https://reviews.llvm.org/D33283

llvm-svn: 303848