Thread analyzer: Prevent on POSIX ARCH

The thread analyzer cannot be really used with the
POSIX architecture.

As:
* Code takes 0 simulated time to execute.
  So the analyzer will report 0 cycles being used.
* The stack allocated by Zephyr is not actually used
  (except for a tiny part used by the arch code itself
  to do a bit of thread bookkeeping).
  The POSIX architecture uses a separate stack
  (from an underlying Linux pthread) which Zephyr is blind
  about. So the thread analyzer is going to only report
  a tiny stack utilization.

Prevent users from selecting them together to avoid confusion.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>