.md macro patch (1/3)

[Zack Weinberg]

I feel capable of approving your two preliminary patches:

> 	* read-rtl.c (string_obstack): New file-scope variable.
> 	(read_string, read_quoted_string, read_braced_string)
> 	(read_escape): Remove obstack parameter and use string_obstack instead.
> 	(read_rtx): Remove function-local rtl_obstack and initialize
> 	string_obstack instead.  Update call to read_string.

and

> 	* read-rtl.c (read_rtx): Tidy use of format_ptr.

Go ahead and check these in.

zw