Introduce sigtimedwait() and sigwaitinfo()

This change also invents sigcountset() and strsignal_r() and improves
the quality of siginfo_t handling.

libc/calls/sigwaitinfo.c

@@ -0,0 +1,33 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/sigtimedwait.h"
+
+/**
+ * Waits for signal synchronously.
+ *
+ * @param set is signals for which we'll be waiting
+ * @param info if not null shall receive info about signal
+ * @return signal number on success, or -1 w/ errno
+ * @raise EINTR if an asynchronous signal was delivered instead
+ * @raise ENOSYS on OpenBSD, XNU, and Windows
+ * @see sigtimedwait()
+ */
+int sigwaitinfo(const sigset_t *mask, siginfo_t *si) {
+  return sigtimedwait(mask, si, 0);
+}