enhanced c++ compiler detection

qse/m4/ax_cxx_namespace.m4

@@ -0,0 +1,25 @@
+dnl @synopsis AX_CXX_NAMESPACE_STD
+dnl
+dnl If the compiler supports namespace std, define
+dnl HAVE_CXX_NAMESPACE_STD.
+dnl
+dnl @category Cxx
+dnl @author Todd Veldhuizen
+dnl @author Luc Maisonobe <luc@spaceroots.org>
+dnl @version 2004-02-04
+dnl @license AllPermissive
+
+AC_DEFUN([AX_CXX_NAMESPACE_STD], [
+  AC_CACHE_CHECK(if c++ supports namespace std,
+  ax_cv_cxx_have_std_namespace,
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  AC_TRY_COMPILE([#include <iostream>
+		  std::istream& is = std::cin;],,
+  ax_cv_cxx_have_std_namespace=yes, ax_cv_cxx_have_std_namespace=no)
+  AC_LANG_RESTORE
+  ])
+  if test "$ax_cv_cxx_have_std_namespace" = yes; then
+    AC_DEFINE(HAVE_CXX_NAMESPACE_STD,,[Define if c++ supports namespace std. ])
+  fi
+])