Eliminate some unused function result warnings.
* lib/unused-result.h: New file, defines function attribute macro
__attribute_warn_unused_result__.
* lib/Makefile.am (EXTRA_DIST): Add unused-result.h.
* find/ftsfind.c (find): Issue a diagnostic if fts_close fails,
change return type to bool and return false for this case. Add
__warn_unused_result__ attribute.
(process_all_startpoints): Likewise (except no need for second
diagnostic).
(main): If process_all_startpoints failed, don't do the cleanup
operations because we don't know what subdirectory we're in.
* find/util.c (fd_leak_check_is_enabled): Avoid implicit
pointer-to-int conversion.
* lib/buildcmd.c: #include <stdlib.h> for declaration of free.
Signed-off-by: James Youngman <jay@gnu.org>