Having a full VPATH for the srcdir sometimes causes make to grab the
wrong prerequisite for a rule, in particular if we have a file in the
srcdir and also generate a file of the same name in the objdir. We don't
really need VPATH anymore though, since most of the information comes
from mozbuild, where we can explicitly list the path to the srcdir or
objdir as necessary.
Differential Revision: https://phabricator.services.mozilla.com/D42968
--HG--
extra : moz-landing-system : lando
