Remove dependency on platform header paths

The tests and examples should not need these paths.

(cherry picked from commit d74c1811)

examples/CMakeLists.txt

 
 link_libraries(glfw)
 
-include_directories(${glfw_INCLUDE_DIRS} "${GLFW_SOURCE_DIR}/deps")
+include_directories("${GLFW_SOURCE_DIR}/deps")
 
 if (MATH_LIBRARY)
     link_libraries("${MATH_LIBRARY}")

tests/CMakeLists.txt

 
 link_libraries(glfw)
 
-include_directories(${glfw_INCLUDE_DIRS} "${GLFW_SOURCE_DIR}/deps")
+include_directories("${GLFW_SOURCE_DIR}/deps")
 
 if (MATH_LIBRARY)
     link_libraries("${MATH_LIBRARY}")