rhbz#908674: Adapt rtl::Allocator::construct to C++11

...otherwise, at least with some --with-system-boost versions and C++11
compilers, like with Fedora's boost-1.50.0-4.fc18.x86_64 and
gcc-c++-4.7.2-8.fc18.x86_64, using this to copy-construct an instance of
boost::unordered::detail::ptr_node<std::pair<rtl::OUString,Bootstrap_Impl*>> in
the call to p_bootstrap_map->insert(...) in rtl_bootstrap_args_open
(sal/rtl/source/bootstrap.cxx) would memcopy the ptr_node and fail to call
rtl_uString_acquire, leading to memory corruption later on when
rtl_uString_release is called one time too often.

It is not entirely clear to me whether this is a shortcoming of the given Boost
version, but this patch solves the problem and brings rtl::Allocator::construct
in line with the (changed) Allocator requirements of C++11 anyway.

The problem potentially lurks with every use of rtl::Allocator, but only showed
now begining with LO 4.0 where e5111574fd904b38a3980ca4ea3d21cfcb22dea6 "Revert
'sb140: sb140: #i116981# clean up memory upon exit'" re-introduced code into
rtl_bootstrap_args_open that inserts into a boost::unordered_map that uses
rtl::Allocator.

Change-Id: I3be22f59a8eb49d31458480c27f3ce15803c7fd4

config_host/config_global.h.in

@@ -14,6 +14,7 @@ Any change in this header will cause a rebuild of almost everything.
 
 #undef HAVE_CXX11_DELETE
 #undef HAVE_CXX11_OVERRIDE
+#undef HAVE_CXX11_PERFECT_FORWARDING
 #undef HAVE_GCC_BUILTIN_ATOMIC
 #undef HAVE_SFINAE_ANONYMOUS_BROKEN
 #undef HAVE_THREADSAFE_STATICS

configure.ac

@@ -5785,6 +5785,29 @@ else
     AC_MSG_RESULT([no (C++11 disabled)])
 fi
 
+dnl ===================================================================
+dnl Check for C++11 perfect forwarding support
+dnl ===================================================================
+HAVE_CXX11_PERFECT_FORWARDING=
+AC_MSG_CHECKING([whether $CXX supports C++11 perfect forwarding])
+save_CXXFLAGS=$CXXFLAGS
+CXXFLAGS="$CXXFLAGS $CXXFLAGS_CXX11"
+AC_LANG_PUSH([C++])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+        #include <utility>
+        template<typename T, typename... Args> T * f(Args &&... v) {
+            return new T(std::forward<Args>(v)...);
+        }
+    ]], [[
+        f<int>(0);
+    ]])], [perfect_forwarding=yes], [perfect_forwarding=no])
+AC_LANG_POP([C++])
+CXXFLAGS=$save_CXXFLAGS
+AC_MSG_RESULT([$perfect_forwarding])
+if test "$perfect_forwarding" = yes; then
+    AC_DEFINE([HAVE_CXX11_PERFECT_FORWARDING])
+fi
+
 dnl ===================================================================
 dnl system stl sanity tests
 dnl ===================================================================

sal/inc/rtl/allocator.hxx

@@ -23,6 +23,10 @@
 #include "rtl/alloc.h"
 #include <cstddef>
 
+#if defined LIBO_INTERNAL_ONLY
+#include "config_global.h"
+#endif
+
 /// @cond INTERNAL
 
 //######################################################
@@ -125,10 +129,18 @@ public:
     }
 
     //-----------------------------------------
+#if defined HAVE_CXX11_PERFECT_FORWARDING
+    template< typename... Args >
+    void construct (pointer p, Args &&... value)
+    {
+        new ((void*)p)T(std::forward< Args >(value)...);
+    }
+#else
     void construct (pointer p, const T& value)
     {
         new ((void*)p)T(value);
     }
+#endif
 
     //-----------------------------------------
     void destroy (pointer p)