gas .include and .incbin

This fixes a bug in .include and .incbin where given an absolute path
the -I dirs would be searched for the path.

	* read.c (include_dir_count, include_dir_maxlen): Make them size_t.
	(search_and_open): New function.
	(s_incbin, s_include): Use search_and_open.
	(init_include_dir): New function.
	(add_include_dir): Don't set initial "." dir here.
	* read.h (include_dir_count, include_dir_maxlen): Update.
	(init_include_dir, search_and_open): Declare.
	* as.c (gas_early_init): Call init_include_dir.
	* config/tc-rx.c (rx_include): Avoid warning by using size_t.
	* config/tc-tic54x.c (tic54x_set_default_include): Simplify and
	use notes for include path.
	(tic54x_mlib): Use search_and_open.