Allow unquoted = as the first character in ldscript input_list names

Allow unquoted = as the first character in ldscript input_list names

	* ldlex.l (INPUTLIST): New start condition.
	(comment pattern, ",", "(", ")", "AS_NEEDED")
	({FILENAMECHAR1}{FILENAMECHAR}*, "-l"{FILENAMECHAR}+)
	(quoted string pattern, whitespace pattern): Add INPUTLIST to
	valid start conditions.
	(<INPUTLIST>"="{FILENAMECHAR1}{FILENAMECHAR}*): New NAME rule.
	(ldlex_inputlist): New start-condition-setter function.
	* ldgram.y (input_list1): Rename from input_list.  All recursive
	use changed.
	(input_list): New wrapper rule for input_list1, setting
	INPUTLIST lexer state for the duration of parsing input_list1.

All this to say INPUT(=/path/to/file) and not be forced to use
INPUT("=/path/to/file") whenever there's a need to force a sysroot-
prefix.  Still, IMHO it seems better to make use of a previously
invalid syntax and not only change the meaning of quoted =-prefixed
paths (though arguably that's not very useful before this patchset).

This got a little bit hairier than I'd expected: I had to add a new
lexer state (aka. start condition) to avoid a first "=" being lexed as
the token "=", despite that not making sense in constructs expecting
file-names in the first place.  (The grammar doesn't allow for
expressions in any part of those lists.)  I guess I *could* have made
it work using that token anyway, but I didn't like the idea that you
would be able to separate the "=" from the rest of the file-name with
whitespace.