[Release][Bugfix] Fix __cxa_demangle() on recent clang

The test for __cxa_demangle(), which is used by Dune::className() to
demangle type names, doesn't work on my clang 3.6. Apparently, clang
requires the user to include <typeinfo> before <cxxabi.h>. While
classname.hh already does this, the build system tests don't, causing the
feature to get disabled on clang.

Fixed by adding the include to the build system tests.

cmake/modules/DuneCxaDemangle.cmake

@@ -8,7 +8,8 @@
 # perform tests
 include(CheckCXXSourceCompiles)
 
-CHECK_CXX_SOURCE_COMPILES("#include <cxxabi.h>
+CHECK_CXX_SOURCE_COMPILES("#include <typeinfo>
+#include <cxxabi.h>
 int main(void){
     int foobar = 0;
     const char *foo = typeid(foobar).name();

m4/dune_cxa_demangle.m4

@@ -4,6 +4,7 @@ AC_DEFUN([DUNE_CHECK_CXA_DEMANGLE],[
     AC_CACHE_CHECK([for abi::__cxa_demangle], dune_cv_cxa_demangle, [
         AC_LANG_PUSH([C++])
         AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+    #include <typeinfo>
     #include <cxxabi.h>
             ]],
             [[