The functions are now defined under their core names. To avoid code
bloat, I've defined the suffixed names as aliases of the core names.
Both symbols will be globally defined with the same value, and in the
dylib both will be exported.
Fix the default API version when none is given. Zero is the same as
`VK_API_VERSION_1_0`. Prior to this, we were overwriting it with zero if
no app info were given, or if it were zero in the app info. It wasn't
important before, but now that we gate API availability on maximum
Vulkan version, we need to make sure it's a valid version.
On iOS, only compile IOSurface support, and link IOSurface framework to
libMoltenVK.dylib, if IPHONEOS_DEPLOYMENT_TARGET is at least iOS 11.0.
Update to latest version of SPIRV-Cross.
Update MoltenVK version to 1.0.15.
