AC_PROG_F77 should stop when therer is no F77

[Sylvestre Ledru]

Hello,

When I create a configure.ac file which only contains :
AC_INIT
AC_PROG_F77()

When I do a ./configure and despite the fact that there is no fortran
compiler on the computer, it stills try to check the output file name.

checking for g77... no
checking for f77... no
checking for xlf... no
checking for frt... no
[...]
checking for ifc... no
checking for efc... no
checking for pgf95... no
checking for lf95... no
checking for ftn... no
checking for Fortran 77 compiler default output file name...
configure: error: Fortran 77 compiler cannot create executables
See `config.log' for more details.

Maybe it is a normal behaviour but I would like to be able to "catch"
this issue in order to display a nice error et more explicit message
like "You must have a fortran compiler"

Cheers,
Sylvestre