tcg: Add TCG_COND_NEVER, TCG_COND_ALWAYS

tcg: Add TCG_COND_NEVER, TCG_COND_ALWAYS

There are several cases that can be handled easier inside both
translators and code generators if we have out-of-band values
for conditions.  It's easy enough to handle ALWAYS and NEVER in
the natural way inside the tcg middle-end.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>