[tlbuild] asymptote trials

[Karl Berry]

    Is g++ 4.2.1 "old enough"? Because it fails here with
    In file included from path3.cc:10:
    path3.h:386: error: redefinition of ‘struct GC_type_traits<camp::solvedKnot>’
    path.h:456: error: previous definition of ‘struct
    GC_type_traits<camp::solvedKnot>’

yes, that is precisely the error message which is remedied by adding
-DBROKEN_COMPILER.

(-DOMIT_SOLVEDKNOT_DECL was just my temporary name, but John preferred
-DBROKEN_COMPILER, so that's what is there now.)