global labels MUST start with an underscore
local labels SHOULD NOT start with an underscore
global labels are subject to address fixup, which is done for subroutine
calls (bsr) and for the "set_addr" op, but not for normal branches.
The identifier of a ".sub" directive is used as the label for subroutine
calls and normally the sub entry so it must have an underscore, if the
subroutine should be reachable.
Languages in tree, that might need changes:
- jako unknown
- perl6 is ok