thread_pthread.c (rb_reserved_fd_p): false-positive on negative FD

Negative-numbered FDs are never valid FDs on POSIX-like
platforms, and we initialize our self-pipes/eventfd values
to "-1", so stop treating -1 as a reserved FD if our system
is too low on resources to allocate FDs at startup.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65832 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_pthread.c

@@ -1842,6 +1842,10 @@ ruby_stack_overflowed_p(const rb_thread_t *th, const void *addr)
 int
 rb_reserved_fd_p(int fd)
 {
+    /* no false-positive if out-of-FD at startup */
+    if (fd < 0)
+        return 0;
+
 #if UBF_TIMER == UBF_TIMER_PTHREAD
     if (fd == timer_pthread.low[0] || fd == timer_pthread.low[1])
         goto check_pid;