Build fails on Mac from (at least) revision 2457 (Bug #46)

Build fails on Mac Snow Leopard, with the following messages:

/Users/michel/macCode/opencv-2.0/src/ml/mlrtrees.cpp:42:17: error: omp.h: No such file or directory
/Users/michel/macCode/opencv-2.0/src/ml/mlrtrees.cpp:42:17: error: omp.h: No such file or directory
/Users/michel/macCode/opencv-2.0/src/ml/mlertrees.cpp:42:17: error: omp.h: No such file or directory
/Users/michel/macCode/opencv-2.0/src/ml/mltree.cpp:43:17: error: omp.h: No such file or directory
/Users/michel/macCode/opencv-2.0/src/cv/cvcascadedetect.cpp:45:17: error: omp.h: No such file or directory
maker2: * [src/ml/CMakeFiles/ml.dir/mlertrees.o] Error 1
maker2: [src/cv/CMakeFiles/cv.dir/cvcascadedetect.o] Error 1
maker2: Waiting for unfinished jobs....
maker2: [src/ml/CMakeFiles/ml.dir/mltree.o] Error 1
maker1: [src/ml/CMakeFiles/ml.dir/all] Error 2
maker1: Waiting for unfinished jobs....
maker1: ** [src/cv/CMakeFiles/cv.dir/all] Error 2

Builds were fine until recently, last working version was about a week ago (not sure which revision). I have used cmake to set SELECT_OPENMP = OFF, so this really confuses me...