Update the build rules to:
 • Atomically replace the target files to avoid race conditions while
   building.
 • Not distribute the generated files, as they are generated.
 • Use template files instead of putting C and escaped newlines in
   Makefile.am in some grotesque display of nesting.
 • Rename from event-factory-builtins.[ch] to enums.[ch] to more
   accurately reflect what they contain.

This might fix https://bugzilla.redhat.com/show_bug.cgi?id=1403508.