Draco requires default visibility on gcc/clang

CMakeLists.txt

@@ -602,6 +602,10 @@ ELSE()
           "-Wno-sign-compare"
           "-Wno-unused-local-typedefs"
         )
+        # Draco 1.4.1 does not explicitly export any symbols under GCC/clang
+        list(APPEND DRACO_CXX_FLAGS
+          "-fvisibility=default"
+        )
       ENDIF()
       
       ADD_SUBDIRECTORY( "contrib/draco" )