The unused variables when FLOAT_MIXENG is defined caused warnings on
Apple clang version 13.1.6 (clang-1316.0.21.2).

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220316061053.60587-1-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>