[newlib-cygwin] Cygwin: serial: try fix o_nonblock

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=57a80207ff5f7045a45668cee827ce7f6906ccc8

commit 57a80207ff5f7045a45668cee827ce7f6906ccc8
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Thu Mar 12 16:07:01 2020 +0100

    Cygwin: serial: try fix o_nonblock

Diff:
---
 winsup/cygwin/fhandler_serial.cc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/winsup/cygwin/fhandler_serial.cc b/winsup/cygwin/fhandler_serial.cc
index 69e5768f6..f92fc7039 100644
--- a/winsup/cygwin/fhandler_serial.cc
+++ b/winsup/cygwin/fhandler_serial.cc
@@ -68,6 +68,16 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
 	goto err;
       else if (ev)
 	termios_printf ("error detected %x", ev);
+      else if (is_nonblocking ())
+	{
+	  if (!st.cbInQue)
+	    {
+	      tot = -1;
+	      set_errno (EAGAIN);
+	      goto out;
+	    }
+	  inq = st.cbInQue;
+	}
       else if (st.cbInQue && !vtime_)
 	inq = st.cbInQue;
       else if (!is_nonblocking () && !overlapped_armed)