Make the stop-on-sharedlibrary-events setting work.

The StopInfoBreakpoint::PerformAction was overriding the synchronous
breakpoint's ShouldStop report.  Fix that and add a test.

This fixes two bugs in the original submission:
1) Actually generate both dylibs by including the second one in the Makefile
2) Don't ask synchronous callbacks for their opinion on whether to stop
   in the async context, that info is taken care of by recording the m_should_stop
   on entry to PerformAction.

Differential Revision: https://reviews.llvm.org/D98914