gcc.c (option_map): New flag -no-canonical-prefixes.

	* gcc.c (option_map): New flag -no-canonical-prefixes.
	* (display_help): Print help text for new flag.
	* (process_command): Move options translation and language specifics
	and handle new flag early.  Use it to set a function pointer to a
	prefix builder.  Replace make_relative_prefix calls with calls to
	the function pointed to.  Ignore new flag in regular options handling.
	* doc/invoke.texi (Overall Options): Documented -no-canonical-prefixes.

From-SVN: r149702