Require clean-core target and link glow against it

Unless I'm missing something, this seems to be required.

glow-extras has a similar dependency check.

CMakeLists.txt

@@ -209,6 +209,12 @@ if(TARGET glm)
     target_compile_definitions(glow PUBLIC GLOW_HAS_GLM)
 endif()
 
+# clean-core
+if (NOT TARGET clean-core)
+    message(FATAL_ERROR "[glow] requires clean-core")
+endif()
+target_link_libraries(glow PUBLIC clean-core)
+
 # typed geometry
 if(TARGET typed-geometry)
     target_link_libraries(glow PUBLIC typed-geometry)