Does parallel make require guards against duplicate actions?

The old Gen_fmgrtab.sh script used temporary file names that included
its process PID.  It had this comment about that:

# We use the temporary files to avoid problems with concurrent runs
# (which can happen during parallel make).

The new implementation uses temp files that just have ".tmp" appended to
the target file name.  If there is a risk that "make -j" will run the
same action twice in parallel, this isn't good enough.  While it
wouldn't be too tough to add the PID to the scripts, I wonder whether
this comment is about a real problem or just a flight of fancy.  It
doesn't seem to me that parallel make ought to be stupid enough to
do the same action twice.  Anybody know?
        regards, tom lane