[tlbuild] Help with building asymptote

[Karl Berry]

    builtin.cc: In function 'void trans::base_venv(trans::venv&)':
    builtin.cc:1141: error: 'gsl_sf_ellint_Pcomp' was not declared in this scope
    builtin.cc:1141: error: no matching function for call to 'addGSLDOUBLE2Func(const char [2], const char [2], const char [2])'

Add --disable-gsl to the configure command.

I still owe a recipe for building asymptote ...