scripts: Add ifdef protection to non_wsi ext APIs
scripts: Add ifdef protection to non_wsi ext APIs

Dispatch_table_helper.h should not be platform dependent, wrap all
platform dependencies in pre-processor directives for safe
compilation.

Change-Id: I6c876efaceb4d3c38c719f1db9e93d7bd543370e

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