exec-all: extract tb->tc_* into a separate struct tc_tb

exec-all: extract tb->tc_* into a separate struct tc_tb

In preparation for adding tc.size to be able to keep track of
TB's using the binary search tree implementation from glib.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>