[newlib-cygwin] Fix return value on aio_read/write success

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=b1952c03a8d6970f0fb4bcfffb9cfb5b525884d6

commit b1952c03a8d6970f0fb4bcfffb9cfb5b525884d6
Author: Mark Geisert <mark@maxrnd.com>
Date:   Mon Aug 6 22:54:06 2018 -0700

    Fix return value on aio_read/write success
    
    Internally track resultant byte counts as ssize_t, but return 0 as int
    for success indication, per POSIX.

Diff:
---
 winsup/cygwin/aio.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/aio.cc b/winsup/cygwin/aio.cc
index fe63dec..7d5d982 100644
--- a/winsup/cygwin/aio.cc
+++ b/winsup/cygwin/aio.cc
@@ -265,7 +265,7 @@ aiowaiter (void *unused)
     }
 }
 
-static int
+static ssize_t
 asyncread (struct aiocb *aio)
 { /* Try to initiate an asynchronous read, either from app or worker thread */
   ssize_t       res = 0;
@@ -296,7 +296,7 @@ asyncread (struct aiocb *aio)
   return res;
 }
 
-static int
+static ssize_t
 asyncwrite (struct aiocb *aio)
 { /* Try to initiate an asynchronous write, either from app or worker thread */
   ssize_t       res = 0;
@@ -712,7 +712,7 @@ aio_read (struct aiocb *aio)
       ; /* I think this is not possible */
     }
 
-  return res;
+  return res < 0 ? (int) res : 0; /* return 0 on success */
 }
 
 ssize_t
@@ -902,7 +902,7 @@ aio_write (struct aiocb *aio)
       ; /* I think this is not possible */
     }
 
-  return res;
+  return res < 0 ? (int) res : 0; /* return 0 on success */
 }
 
 int