- Renamed option to `builtin_vulkan`, since that's the name of the
library and if we were to add new components, we'd likely use that
same option.
- Merge `vulkan_loader/SCsub` in `vulkan/SCsub`.
- Accordingly, don't use built-in Vulkan headers when not building
against the built-in loader library.
- Drop Vulkan registry which we don't appear to need currently.
- Style and permission fixes.
MinGW-w64 ships all Windows SDK headers as lowercase, which prevents
cross-compiling this code from Linux.
Windows filesystems are case insensitive so it should work fine with
lowercase includes.
PR'ed upstream: https://github.com/KhronosGroup/Vulkan-Loader/pull/212
