Fix PR gdb/23558: Use system's 'getcwd' when cross-compiling GDB
    
    This is a backport of a gnulib fix for the following bug:
    
      https://sourceware.org/bugzilla/show_bug.cgi?id=23558
    
    The problem reported there is about the replacement of 'getcwd' when
    cross-compiling GDB.  With our current gnulib copy, the mechanism for
    deciding whether to use the system's 'getcwd' or gnulib's version is
    too simplistic and pessimistic, so when cross-compiling we always end
    up using gnulib's version, which has a limitation: it cannot handle
    the situation when the parent directory doesn't have read permissions.
    
    The solution is to backport the following gnulib commit:
    
      commit a96d2e67052c879b1bcc5bc461722beac75fc372
      Author: Bruno Haible <bruno@clisp.org>
      Date:   Thu Aug 23 21:13:19 2018 +0200
    
          getcwd: Add cross-compilation guesses.
    
    gdb/ChangeLog:
    2018-09-10  Sergio Durigan Junior  <sergiodj@redhat.com>
    
    	PR gdb/23555
    	PR gdb/23558
    	* gnulib/import/m4/getcwd-path-max.m4: Add cross-compilation
    	guesses.