gdb.c++/userdef.cc: Place comments on the lines to which the
marker function might return.
* gdb.c++/derivation.exp, gdb.c++/overload.exp,
gdb.c++/userdef.exp: Look for those comments to check that we've
returned to the right place, instead of checking line numbers.
* gdb.c++/overload.exp: Select overloadfnarg(void) or overloadfnarg(),
depending on what the symbol table contains.
* gdb.c++/derivation.exp: Accept both "foo(void)" and "foo()" in
the output of the ptype command. Similarly, accept both "const &"
and "const&".