message: Fix cmake library path for libpng16.a
diff: # limitations under the License.
  # ==============================================================================
  include (ExternalProject)
  +include (GNUInstallDirs)
  set(png_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/external/png_archive)
  set(png_URL https://mirror.bazel.build/github.com/glennrp/libpng/archive/v1.6.34.tar.gz)
  @@ -35,7 +36,7 @@ if(WIN32)
  endif()
  endif()
  else()
  - set(png_STATIC_LIBRARIES ${CMAKE_BINARY_DIR}/png/install/lib/libpng16.a)
  + set(png_STATIC_LIBRARIES ${CMAKE_BINARY_DIR}/png/install/${CMAKE_INSTALL_LIBDIR}/libpng16.a)
  endif()
  set(png_HEADERS
  