gas: generated code/data listing output vs .endr and alike

gas: generated code/data listing output vs .endr and alike

These ending directives are swallowed by buffer_and_nest() and hence
aren't seen by read_a_source_file(). Thus they also weren't announced to
the listing subsystem. That was, when macro expansions are included,
thus misguided to associate possible output resulting from the first
line of the construct being expanded with both the .endr and that first
line (i.e. showing it twice).