If the h5cc or h5pcc commands are not available don't assume that HDF5 cannot...

If the h5cc or h5pcc commands are not available don't assume that HDF5 cannot be used, test it instead. We lose the version string and maybe Fortran support.

m4/ax_lib_hdf5.m4

@@ -22,7 +22,10 @@
 #     yes  - do check for HDF5 library in standard locations.
 #     path - complete path to the HDF5 helper script h5cc or h5pcc.
 #
-#   SWIFT modification: HDF5 is required, so only path is described.
+#   SWIFT modifications: HDF5 is required, so only path is described,
+#   when the h5cc or h5pcc commands are not available, we check if
+#   HDF5 can be used anyway and no macros are defined except HAVE_HDF5
+#   and with_hdf5.
 #
 #   If HDF5 is successfully found, this macro calls
 #
@@ -155,11 +158,37 @@ if test "$with_hdf5" = "yes"; then
         AC_MSG_CHECKING([Using provided HDF5 C wrapper])
         AC_MSG_RESULT([$H5CC])
     fi
-    AC_MSG_CHECKING([for HDF5 libraries])
     if test ! -f "$H5CC" || test ! -x "$H5CC"; then
-        AC_MSG_RESULT([no])
-        AC_MSG_WARN(m4_case(m4_normalize([$1]),
-            [serial],  [
+
+dnl Check if we already have HDF5 for C.
+        AC_CHECK_HEADER([hdf5.h], [ac_cv_hhdf5_h=yes], [ac_cv_hhdf5_h=no], [AC_INCLUDES_DEFAULT])
+        AC_CHECK_LIB([hdf5], [H5Fcreate], [ac_cv_libhdf5=yes],
+                     [ac_cv_libhdf5=no])
+        if test "$ac_cv_hhdf5_h" = "yes" && test "$ac_cv_libhdf5" = "yes" ; then
+
+dnl Can compile and link, so we have a HDF5, just don't know which version.
+            AC_MSG_CHECKING([for HDF5 libraries])
+            AC_MSG_RESULT([yes])
+            with_hdf5="yes"
+            HDF5_VERSION="unknown"
+            HDF5_LIBS="-lhdf5"
+ 	    AC_SUBST([HDF5_VERSION])
+	    AC_SUBST([HDF5_CC])
+	    AC_SUBST([HDF5_CFLAGS])
+	    AC_SUBST([HDF5_CPPFLAGS])
+	    AC_SUBST([HDF5_LDFLAGS])
+	    AC_SUBST([HDF5_LIBS])
+	    AC_SUBST([HDF5_FC])
+	    AC_SUBST([HDF5_FFLAGS])
+	    AC_SUBST([HDF5_FLIBS])
+	    AC_DEFINE([HAVE_HDF5], [1], [Defined if you have HDF5 support])
+        else
+
+dnl Time to give up.
+            AC_MSG_CHECKING([for HDF5 libraries])
+            AC_MSG_RESULT([no])
+            AC_MSG_WARN(m4_case(m4_normalize([$1]),
+                    [serial],  [
 Unable to locate serial HDF5 compilation helper script 'h5cc'.
 Please specify --with-hdf5=<LOCATION> as the full path to h5cc.
 HDF5 support is being disabled.
@@ -172,9 +201,12 @@ Unable to locate HDF5 compilation helper scripts 'h5cc' or 'h5pcc'.
 Please specify --with-hdf5=<LOCATION> as the full path to h5cc or h5pcc.
 HDF5 support is being disabled.
 ]))
-        with_hdf5="no"
-        with_hdf5_fortran="no"
+            with_hdf5="no"
+            with_hdf5_fortran="no"
+        fi
     else
+        AC_MSG_CHECKING([for HDF5 libraries])
+
         dnl Get the h5cc output
         HDF5_SHOW=$(eval $H5CC -show)