My bad. I thought you were debugging swift executables, not the swift compiler itself.
Looking at your log, it seems that gdb is hitting an assertion:
/build/gdb-QP3A9N/gdb-8.1/gdb/breakpoint.c:13230: internal-error: void delete_breakpoint(breakpoint*): Assertion `bpt != NULL' failed.
I do recommend you to report this to them, as it's probably the best course of action.