initial stop. The code was using PrivateResume when it should have
used Resume.
This was allowing expression evaluation while the target was running,
and though that was caught a litle later on, we should never have gotten
that far. To make sure that this is caught immediately I made an error
SBValue when this happens, and test that we get this error.
Differential Revision: https://reviews.llvm.org/D144665
a92f7832f3