Generation steps fails when OPENGL_INCLUDE_DIRS is a list

[rezahousseini]

When calling find_package( OpenGL REQUIRED ) the variable OPENGL_INCLUDE_DIRS can return more than one directory. This causes a failure in the call to bindgen (

OCP/CMakeLists.txt

Line 118 in d69b064

-i ${OPENGL_INCLUDE_DIRS}

) where it is assumed that the variable only contains one directory.