Make improvements

- Document redbean's argon2 module
- Fix regressions in cthreads library
- Make testlib work better with threads
- Give the cthreads library lots of love
- Remove some of the stdio assembly code
- Implement getloadavg() across platforms
- Code size optimizations for errnos, etc.
- Only check for signals in main thread on Windows
- Make errnos for dup2 / dup3 consistent with posix

This change also fixes a bug in the argon2 module, where the NUL
terminator was being included in the hash encoded ascii string. This
shouldn't require any database migrations to folks who found this module
and productionized it, since the argon2 library treats it as a c string.

libc/stdio/fgetwc_unlocked.c

@@ -0,0 +1,51 @@
+/*-*- 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 2020 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/stdio/stdio.h"
+#include "libc/str/thompike.h"
+#include "libc/str/tpdecodecb.internal.h"
+
+/**
+ * Reads UTF-8 character from stream.
+ * @return wide character or -1 on EOF or error
+ */
+wint_t fgetwc_unlocked(FILE *f) {
+  int c, n;
+  wint_t b, x, y;
+  if (f->beg < f->end) {
+    b = f->buf[f->beg++] & 0xff;
+  } else if ((c = fgetc_unlocked(f)) != -1) {
+    b = c;
+  } else {
+    return -1;
+  }
+  if (b < 0300) return b;
+  n = ThomPikeLen(b);
+  x = ThomPikeByte(b);
+  while (--n) {
+    if ((c = fgetc_unlocked(f)) == -1) return -1;
+    y = c;
+    if (ThomPikeCont(y)) {
+      x = ThomPikeMerge(x, y);
+    } else {
+      ungetc_unlocked(y, f);
+      return b;
+    }
+  }
+  return x;
+}