mlresampler_undated.cpp.o should require OpenMP

[tbigot]

/home/anc/src/ALE/src/mlresampler_undated.cpp:5:17: fatal error: omp.h: No such file or directory
#include <omp.h>
                 ^
compilation terminated.
src/CMakeFiles/mlresampler_undated.dir/build.make:54: recipe for target 'src/CMakeFiles/mlresampler_undated.dir/mlresampler_undated.cpp.o' failed
make[2]: *** [src/CMakeFiles/mlresampler_undated.dir/mlresampler_undated.cpp.o] Error 1
CMakeFiles/Makefile2:356: recipe for target 'src/CMakeFiles/mlresampler_undated.dir/all' failed
make[1]: *** [src/CMakeFiles/mlresampler_undated.dir/all] Error 2
Makefile:76: recipe for target 'all' failed
make: *** [all] Error 2