gas: macros nested too deep error

.macro r;r;.endm;r

Currently reports:
nest.s: Assembler messages:
nest.s:2: Fatal error: macros nested too deeply
nest.s:2:  Info: macro invoked from here
nest.s:2:   Info: macro invoked from here
...
nest.s:2:<much indenting> Info: macro invoked from here
nest.s:1:<much indenting>  Info: macro invoked from here

This patch corrects the line number reported, and downgrades the error
from as_fatal to as_bad.

	* input-scrub.c (input_scrub_include_sb): Report "macros
	nested too deeply" using as_bad.
	* macro.c (buffer_and_nest): Only bump line number in .lineinfo
	if we have a '\n'.