Add a -mno-dollar-line-separator command line option to the AVR assembler.

Add a -mno-dollar-line-separator command line option to the AVR assembler.

Some frontends, like the gcc Objective-C frontend, emit symbols with $
characters in them.  The AVR target code in gas treats $ as a line separator,
so the code doesn?t assemble correctly.

Provide a machine-specific option to disable treating $ as a line separator.

	* config/tc-avr.c (enum options): Add option flag.
	(struct option): Add option -mno-dollar-line-separator.
	(md_parse_option): Adjust treatment of $ when option is present.
	* config/tc-avr.h: Use avr_line_separator_chars.