Test for the 'final' keyword from C++11

This patch adds an AutoTools test that tests whether the compiler
supports the 'final' keyword.  It defines the DUNE_FINAL preprocessor
macro, which expands to 'final' if the keyword is supported, and
is empty otherwise.

dune/common/final.hh

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+#ifndef DUNE_COMMON_FINAL_HH
+#define DUNE_COMMON_FINAL_HH
+
+/** \file
+ * \brief Definition of the DUNE_FINAL macro, which encapsulates
+ * the 'final' keyword from C++11
+ */
+
+#if ! HAVE_KEYWORD_FINAL
+#define DUNE_FINAL
+#else
+#define DUNE_FINAL final
+#endif
+
+#endif   // DUNE_COMMON_FINAL_HH

m4/Makefile.am

@@ -28,6 +28,7 @@ ALLM4S = 					\
 	dune_common.m4				\
 	dune_compiler.m4			\
 	dune_cxa_demangle.m4			\
+	dune_final.m4				\
 	dune_fortran.m4				\
 	dune_deprecated.m4			\
 	dune_deprecated_cppflags.m4		\

m4/dune_common.m4

@@ -31,6 +31,7 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
   AC_REQUIRE([MAKE_SHARED])
   AC_REQUIRE([DUNE_LINKCXX])
   AC_REQUIRE([DUNE_CHECKDEPRECATED])
+  AC_REQUIRE([DUNE_CHECKFINAL])
   AC_REQUIRE([DUNE_CHECKUNUSED])
   AC_REQUIRE([DUNE_CHECK_CXA_DEMANGLE])
   AC_REQUIRE([DUNE_SET_MINIMAL_DEBUG_LEVEL])

m4/dune_final.m4

+# Check if the 'final' keyword is supported
+
+AC_DEFUN([DUNE_CHECKFINAL],[
+    AC_CACHE_CHECK([for keyword 'final'], dune_cv_keyword_final, [
+        AC_LANG_PUSH([C++])
+        AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+                        struct Foo
+                        {
+                          virtual void foo() final;
+                        };
+                          ]],
+                          [])],
+                        dune_cv_keyword_final="yes",
+                        dune_cv_keyword_final="no")
+        AC_LANG_POP([C++])
+    ])
+
+    AS_IF([test "x$dune_cv_keyword_final" = "xyes"],
+      [AC_DEFINE_UNQUOTED(HAVE_KEYWORD_FINAL,
+                          1,
+                          [does the compiler support the keyword 'final'?])],)
+
+    AH_BOTTOM([#include <dune/common/final.hh>])
+])