This reverts commit 2d6fb5c628,
and adds a fix for Alien::raylib's test failures.
The tests failed because the resulting static library didn't reexport
GLFW symbols. As a fix, we now have GLFW create a CMake "object library"
target that we can link with both the static and shared raylib.
This is arguably ugly... Proper fix would probably be a GLFW upstream
object library target.
Closes#536.