waf: (fixes #2270) Support -std=c++11 by default

RELEASE_NOTES

@@ -18,6 +18,13 @@ This release is not yet available.
 
 Supported platforms
 -------------------
+This release is intended to work on systems with the following minimal
+requirements:
+- g++-4.8 or later
+- clang-3.3 or later
+- Python 2.7 (Python 2 series)
+- Python 3.4 or later (Python 3 series)
+
 This release has been tested on the following platforms:
 
 New user-visible features

wscript

@@ -413,6 +413,9 @@ def configure(conf):
                 conf.report_optional_feature("static", "Static build", False,
                                              "Link flag -Wl,--whole-archive,-Bstatic does not work")
 
+    # Enable C++-11 support
+    env.append_value('CXXFLAGS', '-std=c++11')
+
     # Set this so that the lists won't be printed at the end of this
     # configure command.
     conf.env['PRINT_BUILT_MODULES_AT_END'] = False