Simplify read-md.c and read-rtl.c using require_char_ws

Simplify read-md.c and read-rtl.c using require_char_ws

read-md.c and read-rtl.c repeatedly use this pattern:

    c = read_skip_spaces ();
    if (c != ')')
      fatal_expected_char (')', c);

Simplify them by introduce a helper function to do this.

gcc/ChangeLog:
	* read-md.c (require_char_ws): New function.
	(read_string): Simplify using require_char_ws.
	(handle_constants): Likewise.
	(handle_enum): Likewise.
	(handle_file): Likewise.
	* read-md.h (require_char_ws): New declaration.
	* read-rtl.c (read_conditions): Simplify using require_char_ws.
	(read_mapping): Likewise.
	(read_rtx_code): Likewise.
	(read_nested_rtx): Likewise.

From-SVN: r236101