[CMake] Also set LIBRARY_OUTPUT_DIRECTORY target property.

This is fix to the previous change of using the RUNTIME_OUTPUT_DIRECTORY target property in CMakeLists.txt
MSVC does not have to rely on LIBRARY_OUTPUT_DIRECTORY for shared libraries, i.e. add_library() target, but Linux does.
This fixes the missing libLLGL_*.so libraries in the output directory on Linux.

CMakeLists.txt

@@ -227,6 +227,7 @@ function(set_llgl_module_properties MODULE_NAME)
             DEBUG_POSTFIX               "D"
             FOLDER                      "LLGL"
             RUNTIME_OUTPUT_DIRECTORY    "${LLGL_OUTPUT_DIR}"
+            LIBRARY_OUTPUT_DIRECTORY    "${LLGL_OUTPUT_DIR}"
     )
 endfunction()