Fortran 90 with autoconf questions

[Aleksandar B. Samardzic]

Am using automake 1.4-p5 and autoconf version 2.13 (from RedHat Linux
7.3 actually). Got C library that I would like to have added Fortran 90
interface (interface consists of ona additional C file and one F90
file). However, I am able to test F90 interface only using Intel F90
compiler, so I decided to left interface from library by default and add
--enable-f90-support flag to my configure.in in order to make possible
to users having Intel compiler installed to compile additional two files
thus enabling F90 interface. I was able to accomplish everything
necessary on automake side. I've added following to configure.in:
  AM_CONDITIONAL(ENABLE_F90_SUPPORT, test "$enable_f90_support" = yes)
then include two additional files in Makefile.am's library_la_SOURCES
conditionally. Adding:
  SUFFIXES = .f90
near the top of Makefile.am and:
  F77=ifc
  AC_PROG_F77
("ifc" is name of Intel compiler) to configure.in everything works fine
regarding configuration (with or without F90 interface) and compilation
of librarary. Now I have two questions:
1. Is above right way to go regarding F90 support in auto-tools?
2. I would like now to have AC_PROG_F77 checks executed only if F90
interface required (I don't need these checks if user don't want F90
interface). How to accomplish this?

Thanks.