The tcg_out* and tcg_patch* functions are utility routines that may or
may not be used by a particular backend; mark them with the 'unused'
attribute to suppress spurious warnings if they aren't used.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>