Cmake: fix to make linking work on Ubuntu

cmake/CMakeLists.txt

 # Boilerplate.
 cmake_minimum_required (VERSION 3.3)   # The latest version as I write this.  May be too strict.
 project (skimake)
 set (CMAKE_CXX_STANDARD 11)
 
 # Default to Release mode.  We're mainly targeting Skia users, not Skia developers.
 if (NOT CMAKE_BUILD_TYPE)
     set (CMAKE_BUILD_TYPE Release)
 endif ()
 
@@ skipping 178 matching lines @@
 if (FONTCONFIG_INCLUDE_DIRS AND FONTCONFIG_LIBRARIES)
     list (APPEND private_includes ${FONTCONFIG_INCLUDE_DIRS})
     list (APPEND libs             ${FONTCONFIG_LIBRARIES})
 endif()
 
 if (APPLE)
     find_library(APPLICATION_SERVICES_FRAMEWORK ApplicationServices REQUIRED)
     list (APPEND libs ${APPLICATION_SERVICES_FRAMEWORK})
 endif()
 
+find_package(OpenGL REQUIRED)
+list (APPEND libs  ${OPENGL_LIBRARIES})
+
 # This is our main output, libskia.so.
 # We mostly build an .so here because it helps test we've linked everything,
 # not so much that we think Skia is a good candidate to ship as a shared library.
 add_library (skia SHARED ${srcs})
 
 target_compile_definitions(skia
     PUBLIC
     PRIVATE -DSKIA_DLL)
 
 target_include_directories(skia
     PUBLIC  ${public_includes}
     PRIVATE ${private_includes})
 
 target_link_libraries(skia
     PUBLIC
     PRIVATE ${libs})
 
 
 set_target_properties(skia PROPERTIES
     COMPILE_FLAGS "-fno-exceptions -fno-rtti -Wno-deprecated-declarations"
     CXX_VISIBILITY_PRESET hidden
     VISIBILITY_INLINES_HIDDEN true)
 
 # Now build a simple example app that uses Skia via libskia.so.
-find_package(OpenGL REQUIRED)
 add_executable(example example.cpp)
 target_link_libraries(example skia ${OPENGL_LIBRARIES})