analyzer: split out checker-path.cc into a new checker-event.cc

gcc/ChangeLog:
	* Makefile.in (ANALYZER_OBJS): Add analyzer/checker-event.o.

gcc/analyzer/ChangeLog:
	* checker-event.cc: New file, split out from...
	* checker-path.cc: ...this file.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>