Do no enable MPI support when '--disable-mpi'.

configure.ac

@@ -161,21 +161,22 @@ AC_CHECK_FUNCS([grib_get_length])
 # Compile with MPI support
 AC_ARG_ENABLE([mpi],
   AS_HELP_STRING([--enable-mpi],
-    [Compile with MPI compiler @<:@default=no@:>@]),
-    [enable_mpi=yes
-     ACX_C_PACKAGE([MPI],[mpi.h],,,
-       [AC_MSG_FAILURE([Required header mpi.h not found or not compilable.])
-        enable_MPI=no],[MPI_Waitall],[mpi mpich],,,
-       [AC_MSG_FAILURE([Cannot link C MPI programs.])
-        enable_MPI=no])
-     AS_IF([test -n "$FC" && test "X$FC" != "Xno"],
-       [ACX_FORTRAN_PACKAGE([MPI], [mpif.h],,,
-          [AC_MSG_FAILURE([Required include mpif.h not found or not compilable.])
-           enable_MPI=no],[mpi_waitall],
-          [mpi mpi_f90 mpi_f77 mpich],[[-lmpi_f77 -lmpi],[-lmpi]],,
-          [AC_MSG_FAILURE([Cannot link Fortran MPI programs.])
-           enable_MPI=no],[])])],
+    [Compile with MPI compiler @<:@default=no@:>@]),,
     [enable_mpi=no])
+AS_VAR_IF([enable_mpi], [yes],
+  [ACX_C_PACKAGE([MPI],[mpi.h],,,
+     [AC_MSG_FAILURE([Required header mpi.h not found or not compilable.])
+      enable_MPI=no],
+     [MPI_Waitall],[mpi mpich],,,
+     [AC_MSG_FAILURE([Cannot link C MPI programs.])
+      enable_MPI=no])
+   AS_IF([test -n "$FC" && test "X$FC" != "Xno"],
+     [ACX_FORTRAN_PACKAGE([MPI], [mpif.h],,,
+        [AC_MSG_FAILURE([Required include mpif.h not found or not compilable.])
+         enable_MPI=no],[mpi_waitall],
+        [mpi mpi_f90 mpi_f77 mpich],[[-lmpi_f77 -lmpi],[-lmpi]],,
+        [AC_MSG_FAILURE([Cannot link Fortran MPI programs.])
+         enable_MPI=no],[])])])
 AS_IF([test x"${enable_mpi}" = x"yes"],
       [USE_MPI=yes])
 HAVE_PARALLEL_NC4=0