tcg-alpha: Fix type mismatch errors in cpu_signal_handler.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-alpha: New TCG target.

This began with a patch from Dong Weiyu <cidentifier@yahoo.com.cn>,
and was modified to fix problems and to adapt to changes in TCG.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-alpha: Implement tcg_register_jit