Enable clang++ to use --cpp11.

Signed-off-by: Andrew Paprocki <andrew@ishiboo.com>
[APPROVAL] apaprocki-tools/cpp11-newer-compilers to master
Upgrade to waf 1.8.4.

This version adds support for `clang` and `clang++` compilers on
Linux and OSX so that they can be used directly and not just when
the `gcc` and `g++` commands actually map to Clang.

Tested on Linux, Solaris, AIX, and Windows.

Signed-off-by: Andrew Paprocki <andrew@ishiboo.com>
Fix support for CXX and CC environment variables

Waf 1.8.4 uses the CXX and CC environment variables in ctx.environ
instead of directly from os.environ.  ctx.environ is initialized from
os.environ on start up, so modifying os.environ later will not affect
waf's view of environment variables.  Change bdewscript.py to update
ctx.environ instead of os.environ when updating the values of CC and
CXX.
Patch waf 1.8.4 to fix support for CXX & CC on sun

waf 1.8.0 - 1.8.4 has a bug that prevents CC and CXX environment
variables from being considered when loading sun studio compilers. Patch
this locally until this is officially fixed.
Update waf to head of master branch

Update waf to commit 20a1ed61468cc793c0a79de83ea1b7005de0ce88, which is
currently the head of master in the official waf git repo.

Fixes 3 submitted issues:
https://code.google.com/p/waf/issues/detail?id=1511
https://code.google.com/p/waf/issues/detail?id=1512
https://code.google.com/p/waf/issues/detail?id=1513