Using ./waf didn't solve the problem.
I'm doing it from the core.lv2 directory because I'm creating packages
for Ubuntu.
If I come back to the SVN revision 273, it works fine.
Since 274, I can't do "./waf configure" from the core.lv2 directory.
(doing it from the trunk directory works though...)
Adding the following line the "def options(opt)" of wscript solved the issue:
opt.load('compiler_cxx')
Hope that helps!
Aurélien