Function vkMergeValidationCachesEXT 

pub unsafe extern "system" fn vkMergeValidationCachesEXT(
    device: VkDevice,
    dstCache: VkValidationCacheEXT,
    srcCacheCount: u32,
    pSrcCaches: *const VkValidationCacheEXT,
) -> VkResult

Available if built with prototypes.