Merge 'fix-ssh-hangs-reloaded'

This commit merges the backport of the fix for freezes during Git clones
of large repositories via SSH.

That should fix git-for-windows/git#5682,
git-for-windows/git#5688 and potentially also
git-for-windows/git#5663.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

winsup/cygwin/fhandler/pipe.cc

@@ -561,7 +561,7 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
       ULONG len1;
       DWORD waitret = WAIT_OBJECT_0;
 
-      if (left > chunk && !is_nonblocking ())
+      if (left > chunk && !real_non_blocking_mode)
 	len1 = chunk;
       else
 	len1 = (ULONG) left;