Reapply "Rewrite gdb-remote's SendContinuePacketAndWaitForResponse"

Resumbitting the commit after fixing the following problems:
- broken unit tests on windows: incorrect gtest usage on my part (TEST vs. TEST_F)
- the new code did not correctly handle the case where we went to interrupt the process, but it
  stopped due to a different reason - the interrupt request would remain queued and would
  interfere with the following "continue". I also added a unit test for this case.

This reapplies r277156 and r277139.

llvm-svn: 278118