sleep: work around cygwin bug On cygwin 1.5.x, sleep amounts larger than 49.7 days (2**32 milliseconds) failed instantly, but with a garbage return value from uninitialized memory. * lib/sleep.c (rpl_sleep): Work around the bug. * m4/sleep.m4 (gl_FUNC_SLEEP): Detect the bug. (gl_PREREQ_SLEEP): Delete unused macro. * modules/sleep (Depends-on): Add verify. * m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Add default. * modules/unistd (Makefile.am): Substitute witness. * lib/unistd.in.h (sleep): Update prototype. * doc/posix-functions/sleep.texi (sleep): Document the bug. * tests/test-sleep.c (main) [HAVE_DECL_ALARM]: Test it. * modules/sleep-tests (Depends-on): Check for alarm. Signed-off-by: Eric Blake <ebb9@byu.net>