fix linux/windows opengl include?

Former-commit-id: 34b6ccf513f7fdc875cdd85668fa483fd08b044e

shared/cmake/CMakeLists.txt

@@ -344,6 +344,10 @@ if(LIBIGL_WITH_OPENGL)
       set(GLFW_BUILD_DOCS OFF CACHE BOOL " " FORCE)
       set(GLFW_BUILD_INSTALL OFF CACHE BOOL " " FORCE)
       target_include_directories(igl_opengl_glfw PRIVATE ${GLFW_INCLUDE_DIRS})
+      target_include_directories(igl_opengl_glfw PRIVATE ${OPENGL_INCLUDE_DIR})
+      if(NOT APPLE)
+        target_include_directories(igl_opengl PRIVATE "${LIBIGL_EXTERNAL}/nanogui/ext/glew/include")
+      endif()
     endif()
     list(APPEND LIBIGL_INCLUDE_DIRS ${GLFW_INCLUDE_DIRS})
     list(APPEND LIBIGL_EXTRA_LIBRARIES ${LIBIGL_OPENGL_GLFW_EXTRA_LIBRARIES})