Fix gdb.texinfo for old makeinfo
    
    With old makeinfo (version 4.13) the changes introduced in
    
    commit 2d97a5d9d33aea87c3bd02fd1fa417f5d4e1fa05
    Author:     John Baldwin <jhb@FreeBSD.org>
    
        Document support for 'info proc' on FreeBSD.
    
    fail to build.
    
    gdb/doc/ChangeLog:
    
    	* gdb.texinfo (pwd): Fix whitespace.