I suggest making a new Vulkan project within Gentoo and moving these packages from x11@ maintainership to it:
dev-cpp/robin-hood-hashing dev-util/glslang dev-util/spirv-headers dev-util/spirv-tools dev-util/volk dev-util/vulkan-headers dev-util/vulkan-tools dev-util/vulkan-utility-libraries media-libs/shaderc media-libs/vulkan-layers media-libs/vulkan-loader (I've repeatedly forgotten to clean up shaderc and glslang when I clean up the others because they are the only two that are not maintained by x11@)
