layers/vk_layer_config.cpp: fix win32 include case
layers/vk_layer_config.cpp: fix win32 include case

Fixes mingw-w64 compilation on case-sensitive file systems.
KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers