tcg: Add support for debugging leakage of temporaries

Add support (if CONFIG_DEBUG_TCG is defined) for debugging leakage
of temporary variables. Generally any temporaries created by
a target while it is translating an instruction should be freed
by the end of that instruction; otherwise carefully crafted
guest code could cause TCG to run out of temporaries and assert.
By calling tcg_check_temp_count() after each instruction we can
check that we are not leaking temporaries in this way.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
