In order to have variable size allocated TCGOp, pass the number
of arguments we use (and would allocate) up to tcg_op_alloc().

This alters tcg_emit_op(), tcg_op_insert_before() and
tcg_op_insert_after() prototypes.

In tcg_op_alloc() ensure the number of arguments is in range.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
[PMD: Extracted from bigger patch]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221218211832.73312-2-philmd@linaro.org>