configure

CPP) to create platform independent files. Unfortunately, that means that
every config.status (or configure) run invariably causes a relink of the
postmaster and also that we can't put these files in the distribution
(usefully). So we make it a little smarter: when the output files already
exist and it notices that it would recreate them in identical form, it
doesn't touch them. In order to avoid re-running the make rule all the time
we update a timestamp file instead.

Update release_prep accordingly. Also make Gen_fmgrtab.sh use the awk that
is detected at configure time, not necessarily named `awk' and have it check
for exit statuses a little better.

In other news... Remove USE_LOCALE from the templates, it was set to `no'
everywhere anyway. Also remove YACC and YFLAGS from the templates, configure
is smart enough to find bison or yacc itself. Use AC_PROG_YACC for that
instead of the hand-crafted code. Do not set YFLAGS to `-d'. The make rules
that need this flag should explicitly invoke it. YFLAGS should be a user
variable. Update the makefiles to that effect.