d-builtins.cc: that was an oversight. will revert after test suite finished....

target.asm_out.can_output_mi_thunk: OK, but this part doesn't work in gcc-4.8:

d_comdat_linkage (thunk_decl);
thunk_node->create_edge (funcn, NULL, 0, CGRAPH_FREQ_BASE);
thunk_node->expand_thunk (false, true);

So what are the consequences if this hunk isn't merged?