fix: add workaround for apple libc

Apple's Libc implementation contains a bug which causees it to ignore
the offset data present in the tm struct in favor of the older heuristic
needed by legacy standards. This workaround temporarily sets the global
timezone so it gets picked up during formatting.

Author: marcin-serwin

src/builtin.c

@@ -1753,7 +1753,21 @@ static jv f_strftime(jq_state *jq, jv a, jv b) {
   const char *fmt = jv_string_value(b);
   size_t alloced = strlen(fmt) + 100;
   char *buf = alloca(alloced);
+#ifdef __APPLE__
+  /* Apple Libc (as of version 1669.40.2) contains a bug which causes it to
+   * ignore the `tm.tm_gmtoff` in favor of the global timezone. To print the
+   * proper timezone offset we temporarily switch the TZ to UTC. */
+  char *tz = getenv("TZ");
+  setenv("TZ", "UTC", 1);
+#endif
   size_t n = strftime(buf, alloced, fmt, &tm);
+#ifdef __APPLE__
+  if (tz) {
+    setenv("TZ", tz, 1);
+  } else {
+    unsetenv("TZ");
+  }
+#endif
   jv_free(b);
   /* POSIX doesn't provide errno values for strftime() failures; weird */
   if (n == 0 || n > alloced)