Are there any OpenCV cross compilers available for MICROCONTROLLERs?
OpenCV cross compiler? Errr... I"m not sure such a thing exists! Let's not mix cross-compilers (like gcc), with OpenCV - which is a cross-platform library for computer vision.
But in case you meant OpenCV compiled for microcontrollers, you might find some pre-built binaries for the platform you are working with, but none of these are official releases from the OpenCV developers.
This thread discusses some of the challenges involved when using OpenCV on microcontrollers:
The main issue you will encounter is that OpenCV uses floating point math, and most microcontrollers only have fixed point multipliers, so you will either have to convert some OpenCV code or run floating point emulation on those particular processors, which is probably quite slow.
Some of the posts suggest other less resource consuming alternatives like CImg and CVIPtools.
If you decide to stick with OpenCV, you might be interested in this tutorial: how to building OpenCV for ARM Cortex-A8 platform using Cmake in a linux environment.