FindLua51: do not try to link libm on BeOS

This includes Haiku, which currently is treated as BeOS. The ComplexOneConfig
test already knew about this.
FindGLUT: BeOS does not have libXi and libXmu
FindOpenGL: add Haiku paths

Also check the HP-UX specific paths only when on HP-UX.
Merge topic 'Haiku' into next

0380f36 FindOpenGL: add Haiku paths
8e9630c FindGLUT: BeOS does not have libXi and libXmu
50bfedf FindLua51: do not try to link libm on BeOS