Today, gdbproxy reuses the same buffer for both the qXfer reply and the
actual GDB packet reply.  This worked well, since each byte in the qXfer
reply buffer matched 1:1 to each byte in the actual GDB reply packet.

Since we escape special characters now, this property no longer holds
and a single byte in qXfer reply will take up to two bytes in the GDB
reply packet.  This causes offsets to shift, preventing the
offset/length response slicing (part of GDB protocol) from working
correctly.

Fix this by writing the qXfer reply data in a separate buffer, and
performing slicing out of it.
Signed-off-by: Jinoh Kang <jinoh.kang.kr@gmail.com>
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>