ompi_ext.m4: Allow generated MPI-ext Fortran headers

Allow MPI extensions to generate Fortran headers using Autoconf.

For example, allow following files.

```
ompi/mpiext/example/mpif-h/mpiext_example_mpifh.h.in
ompi/mpiext/example/use-mpi/mpiext_example_usempi.h.in
ompi/mpiext/example/use-mpi-f08/mpiext_example_usempif08.h.in
```

Generated MPI extension C headers are already allowed in commit
6a7d527.

Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>

Author: kawashima-fj

config/ompi_ext.m4

@@ -506,7 +506,7 @@ EOF
 
     AC_MSG_CHECKING([if MPI Extension $component has mpif.h bindings])
 
-    if test -e "$test_header" ; then
+    if test -e "$test_header" || test -e "$test_header".in ; then
         AC_MSG_RESULT([yes])
         enabled_mpifh=1
 
@@ -541,6 +541,10 @@ EOF
                AC_MSG_ERROR([Cannot continue])])
 
         component_header="mpiext_${component}_mpifh.h"
+        mpifh_component_header_path="ompi/mpiext/$component/mpif-h/${component_header}"
+        if test -e "${srcdir}/${mpifh_component_header_path}" ; then
+            mpifh_component_header_path="${srcdir}/${mpifh_component_header_path}"
+        fi
 
         cat >> $mpif_ext_h <<EOF
 !
@@ -577,12 +581,17 @@ EOF
 
     AC_MSG_CHECKING([if MPI Extension $component has "use mpi" bindings])
 
-    if test -e "$test_header" ; then
+    if test -e "$test_header" || test -e "$test_header".in ; then
         AC_MSG_RESULT([yes])
 
         EXT_USEMPI_HEADERS="$EXT_USEMPI_HEADERS mpiext/$component/use-mpi/mpiext_${component}_usempi.h"
         $5="$$5 $component"
+
         component_header="mpiext_${component}_usempi.h"
+        usempi_component_header_path="ompi/mpiext/$component/use-mpi/$component_header"
+        if test -e "${srcdir}/${usempi_component_header_path}" ; then
+            usempi_component_header_path="${srcdir}/${usempi_component_header_path}"
+        fi
 
         cat >> $mpiusempi_ext_h <<EOF
 !
@@ -597,12 +606,12 @@ EOF
         if test "$enabled_mpifh" = 1; then
             mpifh_component_header="mpiext_${component}_mpifh.h"
             cat >> $mpiusempi_ext_h <<EOF
-#include "${srcdir}/ompi/mpiext/$component/mpif-h/$mpifh_component_header"
+#include "${mpifh_component_header_path}"
 EOF
         fi
 
         cat >> $mpiusempi_ext_h <<EOF
-#include "${srcdir}/ompi/mpiext/$component/use-mpi/$component_header"
+#include "${usempi_component_header_path}"
 
 EOF
     else
@@ -628,13 +637,17 @@ EOF
 
     AC_MSG_CHECKING([if MPI Extension $component has "use mpi_f08" bindings])
 
-    if test -e "$test_header" ; then
+    if test -e "$test_header" || test -e "$test_header".in ; then
         AC_MSG_RESULT([yes])
 
         EXT_USEMPIF08_HEADERS="$EXT_USEMPIF08_HEADERS mpiext/$component/use-mpi-f08/mpiext_${component}_usempif08.h"
         $6="$$6 $component"
 
         component_header="mpiext_${component}_usempif08.h"
+        usempif08_component_header_path="ompi/mpiext/$component/use-mpi-f08/$component_header"
+        if test -e "${srcdir}/${usempif08_component_header_path}" ; then
+            usempif08_component_header_path="${srcdir}/${usempif08_component_header_path}"
+        fi
 
         cat >> $mpiusempif08_ext_h <<EOF
 !
@@ -649,12 +662,12 @@ EOF
         if test "$enabled_mpifh" = 1; then
             mpifh_component_header="mpiext_${component}_mpifh.h"
             cat >> $mpiusempif08_ext_h <<EOF
-#include "${srcdir}/ompi/mpiext/$component/mpif-h/$mpifh_component_header"
+#include "${mpifh_component_header_path}"
 EOF
         fi
 
         cat >> $mpiusempif08_ext_h <<EOF
-#include "${srcdir}/ompi/mpiext/$component/use-mpi-f08/$component_header"
+#include "${usempif08_component_header_path}"
 
 EOF
     else