accel/tcg: Add CPU_LOG_EXEC tracing for cpu_io_recompile()

accel/tcg: Add CPU_LOG_EXEC tracing for cpu_io_recompile()

When using -icount, it's useful for the CPU_LOG_EXEC logging
to include information about when cpu_io_recompile() was
called, because it alerts the reader of the log that the
tracing of a previous TB execution may not actually
correspond to an actually executed instruction. For instance
if you're using -icount and also -singlestep then a guest
instruction that makes an IO access appears in two
"Trace" lines, once in a TB that triggers the cpu_io_recompile()
and then again in the TB that actually executes.

(This is a similar reason to why the "Stopped execution of
TB chain before..." logging in cpu_tb_exec() is helpful
when trying to track execution flow in the logs.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20201013122658.4620-1-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>