* make the vector lib compile with opencl/spir (in c++ mode):
  * added FLOOR_CL_CONSTANT, empty for c++/cuda, "constant" for opencl (vars in global scope must be constant values) + use it where necessary (const_math, vector, vector_helper)
  * added explicit load/store functions to the vector class, in opencl mode these also allow loads/stores from/to global or local memory/address-space