AC_PROG_FC([COMPILERS...], [DIALECT])
[COMPILERS...] is a list of specific
compilers you want it to try, so you could give it
[f77 g77] as an argument. That's useful if you
have rather specific demands or need to more-or-less
customize this.
More useful is the DIALECT, which can
be 77, 90, 95 or 2000. Thus if you give this as
AC_PROG_FC([], 77) or
AC_PROG_FC([], 1977) then this will
search only its internal list of Fortran 77 compilers
(which happens to be [g77 f77 xlf frt pgf77 fort77
fl32 af77] currently).