Replace the by-hand method of region identification with
the official user-exec interface. Cross-check the region
provided to the callback with the interval tree from
read_self_maps().
Tested-by: Helge Deller <deller@gmx.de>
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>