Stabilization: fix small typo for yaw autotuning

This prevented the yaw gain autoadjusting, but was
always going to the max level.
Sim Posix: use -D USE_POSIX for consitency with OSX
PiOS Semphore: fix for SIM_OSX

Sim has no ISR methods. This maps them to the normal
non-ISR methods for simulation.
Merge pull request #1273 from peabody124/stabilization_useless_if

Stabilization: fix small typo for yaw autotuning