Better detection for user-requested Fortran bindings.

As discovered by the nightly build, r30379 broke the case where
configure does not find a fortran compiler, and no form of
--enable-mpi-fortran was specified.

This commit specifically calls out the difference between a user
specifying that they want Fortran bindings and the default "try to
compile all the Fortran bindings" cases.

cmr=v1.7.4:ticket=4162

This commit was SVN r30386.

The following SVN revision numbers were found above:
  r30379 --> open-mpi/ompi@7b28af54bb

The following Trac tickets were found above:
  Ticket 4162 --> https://svn.open-mpi.org/trac/ompi/ticket/4162

config/ompi_configure_options.m4

@@ -104,12 +104,18 @@ AC_ARG_ENABLE(mpi-fortran,
     AC_HELP_STRING([--enable-mpi-fortran],
                    [specify which Fortran MPI bindings to build: all (or yes), none (or no), mpifh (build only mpif.h support), usempi (build mpif.h and the mpi module), or usempif08 (build mpifh, the mpi module, and the mpi_f08 module) (default: "all" if Fortran compiler found)]))
 
-AS_IF([test "x$enable_mpi_fortran" = "x"],
-      [enable_mpi_fortran=yes])
-
+OMPI_FORTRAN_USER_REQUESTED=0
 case "x$enable_mpi_fortran" in
+    x)
+        AC_MSG_RESULT([yes (all/default)])
+        OMPI_WANT_FORTRAN_MPIFH_BINDINGS=1
+        OMPI_WANT_FORTRAN_USEMPI_BINDINGS=1
+        OMPI_WANT_FORTRAN_USEMPIF08_BINDINGS=1
+        ;;
+
     xyes|xall)
         AC_MSG_RESULT([yes (all)])
+        OMPI_FORTRAN_USER_REQUESTED=1
         OMPI_WANT_FORTRAN_MPIFH_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPI_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPIF08_BINDINGS=1
@@ -124,6 +130,7 @@ case "x$enable_mpi_fortran" in
 
     xmpifh)
         AC_MSG_RESULT([yes (mpif.h)])
+        OMPI_FORTRAN_USER_REQUESTED=1
         OMPI_WANT_FORTRAN_MPIFH_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPI_BINDINGS=0
         OMPI_WANT_FORTRAN_USEMPIF08_BINDINGS=0
@@ -131,6 +138,7 @@ case "x$enable_mpi_fortran" in
 
     xusempi)
         AC_MSG_RESULT([yes (mpif.h, mpi module)])
+        OMPI_FORTRAN_USER_REQUESTED=1
         OMPI_WANT_FORTRAN_MPIFH_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPI_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPIF08_BINDINGS=0
@@ -138,6 +146,7 @@ case "x$enable_mpi_fortran" in
 
     xusempif08)
         AC_MSG_RESULT([yes (mpif.h, mpi and mpi_f08 modules)])
+        OMPI_FORTRAN_USER_REQUESTED=1
         OMPI_WANT_FORTRAN_MPIFH_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPI_BINDINGS=1
         OMPI_WANT_FORTRAN_USEMPIF08_BINDINGS=1

config/ompi_setup_mpi_fortran.m4

@@ -98,7 +98,7 @@ AC_DEFUN([OMPI_SETUP_MPI_FORTRAN],[
     # Check to see if any of the MPI Fortran bindings were
     # specifically requested.  If so, and we weren't able to setup the
     # Fortran compiler properly, it's an error.
-    AS_IF([test $ompi_fortran_happy -eq 0 -a "$enable_mpi_fortran" = "yes"],
+    AS_IF([test $ompi_fortran_happy -eq 0 -a $OMPI_FORTRAN_USER_REQUESTED -eq 1],
           [AC_MSG_WARN([MPI Fortran bindings requested, but no suitable Fortran compiler found])
           AC_MSG_ERROR([Cannot continue])])