xgetcwd: Port to native Windows.
Use a variant of the gnulib module 'xgetcwd' instead of our own (older) one.
* gnulib-local/lib/xgetcwd.h: Remove file.
* gnulib-local/lib/xgetcwd.c: Remove file.
* gnulib-local/modules/xgetcwd: Remove file.
* gnulib-local/modules/xgetcwd.diff: New file.
* gnulib-local/Makefile.am (EXTRA_DIST): Update.
