[m-rev.] diff: fix source distribution builds

[Zoltan Somogyi]

2020-01-12 23:54 GMT+11:00 Julien Fischer<jfischer at opturion.com>:
>      Restore the .PHONY directives on the Mercury.modules target as their
>      absence is causing the source distribution builds to fail.

What was the symptom?

Zoltan.