Bundle up various global variables within gensupport.c into a
class rtx_reader, with a view towards making it easier to run the
code more than once in-process.

gcc/ChangeLog:
	* genconstants.c (main): Introduce noop_reader and convert call
	to read_md_files to a method call.
	* genenums.c (main): Likewise.
	* genmddeps.c (main): Likewise.
	* genpreds.c (write_tm_constrs_h): Replace use of "in_fname" with
	rtx_reader_ptr->get_top_level_filename ().
	(write_tm_preds_h): Likewise.
	(write_insn_preds_c): Likewise.
	* gensupport.c (class gen_reader): New subclass of rtx_reader.
	(rtx_handle_directive): Convert to...
	(gen_reader::handle_unknown_directive): ...this.
	(init_rtx_reader_args_cb): Convert return type from bool to
	rtx_reader *.  Create a gen_reader instance, using it for the
	call to read_md_files.  Return it if no errors occur.
	(init_rtx_reader_args): Convert return type from bool to
	rtx_reader *.
	* gensupport.h (init_rtx_reader_args_cb): Likewise.
	(init_rtx_reader_args_cb): Likewise.
	* read-md.c (struct file_name_list): Move to class rtx_reader.
	(read_md_file): Delete in favor of rtx_reader::m_read_md_file.
	(read_md_filename): Delete in favor of
	rtx_reader::m_read_md_filename.
	(read_md_lineno): Delete in favor of rtx_reader::m_read_md_lineno.
	(in_fname): Delete in favor of rtx_reader::m_toplevel_fname.
	(base_dir): Delete in favor of rtx_reader::m_base_dir.
	(first_dir_md_include): Delete in favor of
	rtx_reader::m_first_dir_md_include.
	(last_dir_md_include_ptr): Delete in favor of
	rtx_reader::m_last_dir_md_include_ptr.
	(max_include_len): Delete.
	(rtx_reader_ptr): New.
	(fatal_with_file_and_line): Use get_filename and get_lineno
	accessors of rtx_reader_ptr.
	(require_char_ws): Likewise.
	(rtx_reader::read_char): New method, based on ::read_char.
	(rtx_reader::unread_char): New method, based on ::unread_char.
	(read_escape): Use get_filename and get_lineno accessors of
	rtx_reader_ptr.
	(read_braced_string): Use get_lineno accessor of rtx_reader_ptr.
	(read_string): Use get_filename and get_lineno accessors of
	rtx_reader_ptr.
	(rtx_reader::rtx_reader): New ctor.
	(rtx_reader::~rtx_reader): New dtor.
	(handle_include): Convert from a function to...
	(rtx_reader::handle_include): ...this method, converting
	handle_directive from a callback to a virtual function.
	(handle_file): Likewise, converting to...
	(rtx_reader::handle_file): ...this method.
	(handle_toplevel_file): Likewise, converting to...
	(rtx_reader::handle_toplevel_file): ...this method.
	(rtx_reader::get_current_location): New method.
	(parse_include): Convert from a function to...
	(rtx_reader::add_include_path): ...this method, dropping redundant
	update to unused max_include_len.
	(read_md_files): Convert from a function to...
	(rtx_reader::read_md_files): ...this method, converting
	handle_directive from a callback to a virtual function.
	(noop_reader::handle_unknown_directive): New method.
	* read-md.h (directive_handler_t): Delete this typedef.
	(in_fname): Delete.
	(read_md_file): Delete.
	(read_md_lineno): Delete.
	(read_md_filename): Delete.
	(class rtx_reader): New class.
	(rtx_reader_ptr): New decl.
	(class noop_reader): New subclass of rtx_reader.
	(read_char): Reimplement in terms of rtx_reader::read_char.
	(unread_char): Reimplement in terms of rtx_reader::unread_char.
	(read_md_files): Delete.
	* read-rtl.c (read_rtx_code): Update for deletion of globals
	read_md_filename and read_md_lineno.

From-SVN: r240333