[newlib-cygwin] Cygwin: serial: fix GCC warning

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=d2e0b65a7fdc78ed39a8d5338a36cb887805a601

commit d2e0b65a7fdc78ed39a8d5338a36cb887805a601
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Thu Mar 26 14:13:37 2020 +0100

    Cygwin: serial: fix GCC warning
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/fhandler_serial.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler_serial.cc b/winsup/cygwin/fhandler_serial.cc
index 9446315e5..1aaeedf1f 100644
--- a/winsup/cygwin/fhandler_serial.cc
+++ b/winsup/cygwin/fhandler_serial.cc
@@ -80,7 +80,7 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
 	  /* If the number of chars in the inbound queue is sufficent
 	     (minchars defines the minimum), set bytes_to_read accordingly
 	     and don't wait. */
-	  if (st.cbInQue && st.cbInQue >= minchars)
+	  if (st.cbInQue && (ssize_t) st.cbInQue >= minchars)
 	    bytes_to_read = MIN (st.cbInQue, bytes_to_read);
 	}