build: update default CXXFLAGS.

* Add -std=c++03 and -pedantic, and fix the resulting warnings. The
  long-long-int warning is explicitly suppressed because it's not
  trivial to workaround in a platform-independent and ISO-conformant
  way without using C++11.

* Initial support for building with -std=c++11 (experimental).

* Prefer -Og optimization level in debug builds if supported by the
  compiler.

Change-Id: I744a25c8b52842dc3ea3a733d6ab2fa66171e6f8
diff --git a/wscript b/wscript
index 9eab3b1..9681089 100644
--- a/wscript
+++ b/wscript
@@ -37,6 +37,8 @@
              tooldir=['.waf-tools'])
 
     nfdopt = opt.add_option_group('NFD Options')
+    nfdopt.add_option('--with-c++11', action='store_true', default=False, dest='use_cxx11',
+                      help='''Enable C++11 mode (experimental, may not work)''')
     nfdopt.add_option('--with-tests', action='store_true', default=False,
                       dest='with_tests', help='''Build unit tests''')
     nfdopt.add_option('--with-other-tests', action='store_true', default=False,