Fix #922776On ppc64el, altivec.h redefines bool, pixel and vector which can collide with c++ types. This altivec.h inclusion is done by opencl in CL/cl_platform.h . As altivec.h explains, it's possible to undefine those for C++ compatibility in libhmsbeagle/GPU/GPUInterface.h where we don't need them and where it fails, while doing that on the right plateform. Finally, enable libhmsbeagle1v5 on ppc64el.
