Wording in GNU Make manual regarding phony targets

[R. Bernstein]

Recently Bruno Haible point this out from the GNU Make manual:

  A phony target should not be a prerequisite of a real target file;
  if it is, its commands are run every time make goes to update
  that file.  As long as a phony target is never a prerequisite of a
  real target, the phony target commands will be executed only when the
  phony target is a specified goal.

He also observed that in "force" targets this is usually the
situation. Another situation where this doesn't hold would be in those
cases where one tracing, profiling, or debugging code working by
instrumenting/augmenting the Makefile. Given this, I think the wording
above should be changed to something more akin to a heuristic or
guideline.