I put:
using gcc ;
using pything ;

in ~/user-config.jam, but now I get another error.

This is the error from results/bjam.log:

Building Boost.Regex with the optional Unicode/ICU support disabled.
Please refer to the Boost.Regex documentation for more information
(and if you don't know what ICU is then you probably don't need it).
error: Unable to find file or target named
error:     'testwave_app.cpp'
error: referred from project at
error:     '../libs/wave/test/build'


The file is in the directory tree, but either in the wrong place, or bjam 
is not working corectly.

 find -type f -print | egrep testwave_app.cpp
./boost/libs/wave/test/testwave/testwave_app.cpp