Define and propagate CCD_STATIC_DEFINE if the library is compiled as static

[traversaro]

When the ccd library is compiled as static, the CCD_EXPORT should be an empty string, especially on Windows, to avoid linking errors. This can be achieved easily by making sure that CCD_STATIC_DEFINE is defined both when buildng ccd as static, and also when the static ccd is consumed by downstream CMake libraries.

Fix https://github.com/danfis/libccd/issues/33 .