tcg: Move temp_idx and tcgv_i32_temp debug out of line

Removes a multiplicity of calls to __assert_fail, saving up
to 360kiB of .text space as measured on an x86_64 host.

Old     New     Less    %Change
9257272	8888680	368592	3.98%	qemu-system-aarch64
6100968	5911832	189136	3.10%	qemu-system-riscv64
5839112	5707032	132080	2.26%	qemu-system-mips
4447608	4341752	105856	2.38%	qemu-system-s390x

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>