Introduce DUNE_UNUSED as a portable wrapper to __attribute__((unused))

This works pretty much the same way as DUNE_DEPRECATED (without message).

Thanks to Elias Pipping for implementing this.


[[Imported from SVN: r6556]]

dune/common/unused.hh

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+#ifndef DUNE_COMMON_UNUSED_HH
+#define DUNE_COMMON_UNUSED_HH
+
+#ifndef HAS_ATTRIBUTE_UNUSED
+#define DUNE_UNUSED
+#else
+#define DUNE_UNUSED __attribute__((unused))
+#endif
+
+#endif

m4/Makefile.am

@@ -34,6 +34,7 @@ ALLM4S = 					\
 	dune_mpi.m4				\
 	dune_streams.m4				\
 	dune_tr1_headers.m4			\
+	dune_unused.m4			        \
 	fortran_overwrite.m4			\
 	gmp.m4					\
 	hdf5.m4					\

m4/dune_common.m4

@@ -25,6 +25,7 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
   AC_REQUIRE([MAKE_SHARED])
   AC_REQUIRE([DUNE_LINKCXX])
   AC_REQUIRE([DUNE_CHECKDEPRECATED])
+  AC_REQUIRE([DUNE_CHECKUNUSED])
   AC_REQUIRE([DUNE_SET_MINIMAL_DEBUG_LEVEL])
   AC_REQUIRE([DUNE_PATH_XDR])
   AC_REQUIRE([DUNE_MPI])

m4/dune_unused.m4

+# Check if __attribute__((unused)) is supported
+
+AC_DEFUN([DUNE_CHECKUNUSED],[
+    AC_CACHE_CHECK([for __attribute__((unused))], dune_cv_attribute_unused, [
+        AC_LANG_PUSH([C++])
+        AC_TRY_COMPILE([#define UNUSED __attribute__((unused))],
+                       [void f(int a UNUSED, int UNUSED)
+                        {
+                          int b UNUSED;
+                        }],
+                        [],
+                        dune_cv_attribute_unused="yes",
+                        dune_cv_attribute_unused="no")
+        AC_LANG_POP([C++])
+    ])
+
+    AS_IF([test "x$dune_cv_attribute_unused" = "xyes"],
+      [AC_DEFINE_UNQUOTED(HAS_ATTRIBUTE_UNUSED,
+                          1,
+                          [does the compiler support __attribute__((unused))?])],)
+
+    AH_BOTTOM([#include <dune/common/unused.hh>])
+])