There is a not too complicated way to run unit tests under valgrind, kind of
documented in [1].  Basically:

waf --run run-tests --command-template "valgrind %s"

Unfortunately waf does not allow wscripts to add new targets, only new options,
like --valgrind.  So our full range of options is:

1. Do nothing, document the 'waf --run run-tests --command-template "valgrind
%s"' option;

2. Add a waf --valgrindcheck option, which runs the unit tests under valgrind
immediately;

3. Add a waf "configure --enable-valgrind" configure option which turns on
valgrind for when 'waf check' is run in the future;

4. Automatically detect the presence of valgrind during waf configure and use
it for waf check if it was found, unconditionally.

Personally I think 1 is just fine... :-)

[1]
http://www.nsnam.org/wiki/index.php/User_FAQ#How_to_run_NS-3_programs_under_another_tool

I would opt for 2.

Added --valgrind option (waf check --valgrind, or waf --run something
--valgrind).