Forcing FC instead of F77

[Daily, Jeff A]

There is similar mail on this issue "using FC *and* F77, or FC *instead of* 
F77" http://lists.gnu.org/archive/html/autoconf/2006-01/msg00044.html.  But in 
my opinion this was not sufficiently resolved.

We have Fortran 77 code (fixed format, *.f extension only), but we prefer 
Fortran 90 or later compilers since in some cases we want to force INTEGER*8 
promotion with flags e.g. -i8.  We are currently using AC_PROG_F77 with a 
custom list, preferring all known F95 and F90 compilers first and warning the 
user if only F77 is found.  This required copying the guts of AC_PROG_F77 into 
a custom macro and issuing a warning if we only found F77 compilers.

We also have a user requirement that "FC" be the name passed to the command 
line e.g. configure FC=ifort.  I felt a bit dirty doing this, but I modified 
the AC_ARG_VAR use in my custom AC_PROG_F77 to declare FC and FCFLAGS instead 
of F77 and FFLAGS and override the user's F77 and FFLAGS with whatever is set 
for FC and FCFLAGS, respectively.

I thought I was forced to use AC_PROG_F77 since when I used AC_PROG_FC instead, 
I was issued the warning "Fortran 77 source seen but 'F77' is undefined".  I 
was hoping AC_FC_SRCEXT([f]) would help, but I didn't get my hopes up and 
validated it didn't work as hoped.  Yes, it is technically Fortran 77 source, 
but why can't I use AC_PROG_FC in lieu of AC_PROG_F77 without complaints?

Thanks.

Jeff