Compiler [Typechecker]: Added PT_FLAG_CMP_FUN_ARG.
This flag is intended to be used when handling attributes
on types that expand to sequences, do that the handler can
differentiate between matches like
function(__attribute__("foo", mixed)...: mixed)
in the latter case PT_FLAG_CMP_FUN_ARG will be set, so that
the handler can expand the attribute one argument at a time,
and in the former case it will not be set, so that the types
can be joined into a single type.