Compiler: Repurposed reference_inherited_identifier().

The previously unused function reference_inherited_identifier() is
now analogous to the low_* and really_low_* variants, and exported.
Stdio.UDP: Fixed flags handling in set_buffer().

The parsing of the flags argument was broken due to not being
initialized properly. It also used invalid C89 syntax.

Also cleans up the argument parsing by using get_all_args().