istl requires f77

[[Imported from SVN: r5381]]

m4/dune_istl.m4

@@ -8,6 +8,7 @@ AC_DEFUN([DUNE_ISTL_CHECKS],
   AC_REQUIRE([DUNE_PATH_SUPERLU_DIST])
   AC_REQUIRE([DUNE_PARDISO])
   AC_REQUIRE([__AC_FC_NAME_MANGLING])
+  AC_REQUIRE([AC_PROG_F77])
   AC_REQUIRE([ACX_BLAS])
   # add summary entries for tests not maintained by dune
   DUNE_ADD_SUMMARY_ENTRY([METIS],[$with_metis])