layers: Fix Android build
layers: Fix Android build

ndk-bundle/sources/cxx-stl/llvm-libc++/include/set
expects comparator's operator() to be const.

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers