Cygwin: lseek: return ESPIPE rather than EINVAL when called on a fifo

Thanks to Henri for tracking this down:
https://cygwin.com/ml/cygwin/2018-10/msg00062.html

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler.h

@@ -1237,6 +1237,7 @@ class fhandler_fifo: public fhandler_base_overlapped
 public:
   fhandler_fifo ();
   int open (int, mode_t);
+  off_t lseek (off_t offset, int whence);
   int close ();
   int dup (fhandler_base *child, int);
   bool isfifo () const { return true; }

winsup/cygwin/fhandler_fifo.cc

@@ -221,6 +221,14 @@ out:
   return res == success;
 }
 
+off_t
+fhandler_fifo::lseek (off_t offset, int whence)
+{
+  debug_printf ("(%D, %d)", offset, whence);
+  set_errno (ESPIPE);
+  return -1;
+}
+
 bool
 fhandler_fifo::wait (HANDLE h)
 {

winsup/cygwin/release/2.11.2

@@ -0,0 +1,13 @@
+What's new:
+-----------
+
+
+What changed:
+-------------
+
+
+Bug Fixes
+---------
+
+- Return ESPIPE rather than EINVAL from lseek on a fifo.
+  Addresses: https://cygwin.com/ml/cygwin/2018-10/msg00019.html