bullet: fix darwin build

The examples fail with an opengl related issue:

    Undefined symbols for architecture x86_64:
      "SimpleOpenGL3App::SimpleOpenGL3App(char const*, int, int, bool)", referenced from:
          _main in main_opengl_single_example.o
      "_useShadowMap", referenced from:
          GL_ShapeDrawer::drawScene(btDiscreteDynamicsWorld const*, bool, int) in GL_ShapeDrawer.o
    ld: symbol(s) not found for architecture x86_64

And the tests need an extra dependencly, possibley related to
https://github.com/bulletphysics/bullet3/issues/819

    ld: library not found for -lBussIK

/cc ZHF #45961