message: Use constistent warning settings in CMake
  We now use /W4 /WX etc. across all projects defined in CMakeLists,
  including demo and gltfpack; before this change we only applied
  warnings-as-errors to meshoptimizer in CMake builds.
diff: @@ -29,15 +29,15 @@ set(SOURCES
  src/vfetchoptimizer.cpp
  )
  -add_library(meshoptimizer ${SOURCES})
  -target_include_directories(meshoptimizer INTERFACE "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>")
  -
  if(MSVC)
  - target_compile_options(meshoptimizer PRIVATE /W4 /WX)
  + add_compile_options(/W4 /WX)
  else()
  - target_compile_options(meshoptimizer PRIVATE -Wall -Wextra -Werror)
  + add_compile_options(-Wall -Wextra -Wshadow -Wno-missing-field-initializers -Werror)
  endif()
  +add_library(meshoptimizer ${SOURCES})
  +target_include_directories(meshoptimizer INTERFACE "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>")
  +
  if(BUILD_SHARED_LIBS)
  set_target_properties(meshoptimizer PROPERTIES CXX_VISIBILITY_PRESET hidden)
  set_target_properties(meshoptimizer PROPERTIES VISIBILITY_INLINES_HIDDEN ON)
  