(gl_FUNC_GETCWD_PATH_MAX): Renamed from

(gl_FUNC_GETCWD_PATH_MAX): Renamed from
GL_FUNC_GETCWD_PATH_MAX for consistency.  All uses changed.
Use the _ONCE methods, for efficiency.
Check for fcntl.h.  In test program, include <errno.h>
and <fcntl.h> if available.  Remove old K&R cruft from
test program.  Check for common errors in GNU/Linux,
OpenBSD, and Solaris.  Just set gl_cv_func_getcwd_path_max;
don't do AC_LIBOBJ, as that's getcwd.m4's job.