[lldb] Fix exception breakpoint not being resolved when set on dummy target

Summary: Ensure that breakpoint ivar is properly set in exception breakpoint resolver so that exception breakpoints set on dummy targets are resolved once real targets are created and run.

Reviewers: jingham

Reviewed By: jingham

Subscribers: teemperor, JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D69880