gas line buffer handling

gas line buffer handling

This fixes a segfault when macro definitions end on the last line of a
file, and that line isn't properly terminated with a newline.  gas
used to throw away the last line in cases like this, whereas in other
cases gas added the missing newline.  So I've also made gas
consistently provide a missing newline.

	PR gas/18687
	* input-scrub.c (input_scrub_next_buffer): Rearrange and simplify
	loop.  Don't drop lines at end of file lacking a newline, add a
	newline instead.  Ensure partial_size is zero whenever
	partial_where is NULL.  Adjust buffer size for extra char.
	(input_scrub_push, input_scrub_begin): Adjust buffer size here too.