Remove duplicate build of SPIRV-Tools in fetchDependencies.
Remove folder symlinks from Externals and MoltenVKShaderCompiler folders.
Update header search paths to reference External folders directly.
Update External/README.md documentation.
Update MoltenVK version to 1.0.1 to reflect new build instructions.
Minor update to performance logging.
Load external library versions using script instead of Git submodules.
SPIRV-Cross, Vulkan-LoaderAndValidationLayers & VulkanSamples versions recorded in files.
glslang version determined by Vulkan-LoaderAndValidationLayers.
SPIRV-Tools & SPIRV-Headers versions loaded by glslang.
When MoltenVK is built as part of the LunarG SDK, use external libraries
sourced from parent Vulkan-LoaderAndValidationLayers.
Use Vulkan headers from Vulkan-LoaderAndValidationLayers.
No longer generate Vulkan specification.
Update documentation.
