feat(vk): Vk.* - Vulkan 1.0-1.4 generated from the registry, loaded at run time

ludic-dev vkgen reads vk.xml into runtime/native/vk_api.ludic (constants, every struct's
<Struct>_sizeof and <Struct>_<field> offsets, one extern per command) and vk_thunks.ll.
Every size and offset was compiled against the SDK's C headers; `ludic-dev test` checks the
tracked files against the registry wherever the Vulkan SDK is installed.

vk_win.ll (vulkan-1.dll) and vk_mac.ll (libvulkan.1.dylib, MoltenVK) open the loader at run
time, so a program built with Vk.* starts on a machine without Vulkan. ludicc and ludic
build link both for any program that uses Vk.*. The seeds are regenerated for the new
compiler.

vk_probe reports what a machine's Vulkan can do; vk_compute dispatches a Slang compute
shader and reads the picture back, clean under the validation layer on an RTX 3070 Ti and
on an M4 Pro through MoltenVK.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

runtime/native/vk_mac.ll

@@ -0,0 +1,110 @@
+; ============================================================================
+; vk_mac.ll — the Vulkan loader, for macOS, written in LLVM IR.
+;
+; macOS has no Vulkan of its own: the LunarG loader and MoltenVK (Vulkan over
+; Metal) come with the Vulkan SDK or with a game that bundles them. So the loader
+; is looked for at run time - beside the executable, in the usual library
+; directories, then under $VULKAN_SDK - and a Mac without it gets 0 from vk_open
+; and stays on OpenGL. The contract is vk_win.ll's:
+;
+;   lvk_open() -> 1 | 0      lvk_sym(name) -> ptr      lvk_has(name) -> 1 | 0
+;
+; MoltenVK is a portability driver: an instance must ask for
+; VK_KHR_portability_enumeration (and the ENUMERATE_PORTABILITY flag) to see it.
+; ============================================================================
+
+declare ptr @dlopen(ptr, i32)
+declare ptr @dlsym(ptr, ptr)
+declare ptr @getenv(ptr)
+declare i32 @snprintf(ptr, i64, ptr, ...)
+declare i32 @lvk_bind()
+
+@.lvk_c0 = private unnamed_addr constant [18 x i8] c"libvulkan.1.dylib\00"
+@.lvk_c1 = private unnamed_addr constant [35 x i8] c"@executable_path/libvulkan.1.dylib\00"
+@.lvk_c2 = private unnamed_addr constant [33 x i8] c"/usr/local/lib/libvulkan.1.dylib\00"
+@.lvk_c3 = private unnamed_addr constant [36 x i8] c"/opt/homebrew/lib/libvulkan.1.dylib\00"
+@.lvk_env = private unnamed_addr constant [11 x i8] c"VULKAN_SDK\00"
+@.lvk_fmt = private unnamed_addr constant [25 x i8] c"%s/lib/libvulkan.1.dylib\00"
+@lvk_lib  = internal global ptr null
+
+; RTLD_NOW (2) | RTLD_LOCAL (4)
+define internal ptr @lvk_try(ptr %path) {
+entry:
+  %h = call ptr @dlopen(ptr %path, i32 6)
+  ret ptr %h
+}
+
+define i32 @lvk_open() {
+entry:
+  %have = load ptr, ptr @lvk_lib
+  %open = icmp ne ptr %have, null
+  br i1 %open, label %ok, label %t0
+t0:
+  %h0 = call ptr @lvk_try(ptr @.lvk_c0)
+  %n0 = icmp eq ptr %h0, null
+  br i1 %n0, label %t1, label %got0
+got0:
+  store ptr %h0, ptr @lvk_lib
+  br label %bind
+t1:
+  %h1 = call ptr @lvk_try(ptr @.lvk_c1)
+  %n1 = icmp eq ptr %h1, null
+  br i1 %n1, label %t2, label %got1
+got1:
+  store ptr %h1, ptr @lvk_lib
+  br label %bind
+t2:
+  %h2 = call ptr @lvk_try(ptr @.lvk_c2)
+  %n2 = icmp eq ptr %h2, null
+  br i1 %n2, label %t3, label %got2
+got2:
+  store ptr %h2, ptr @lvk_lib
+  br label %bind
+t3:
+  %h3 = call ptr @lvk_try(ptr @.lvk_c3)
+  %n3 = icmp eq ptr %h3, null
+  br i1 %n3, label %t4, label %got3
+got3:
+  store ptr %h3, ptr @lvk_lib
+  br label %bind
+t4:
+  %sdk = call ptr @getenv(ptr @.lvk_env)
+  %nosdk = icmp eq ptr %sdk, null
+  br i1 %nosdk, label %fail, label %t4b
+t4b:
+  %buf = alloca [1024 x i8]
+  %w = call i32 (ptr, i64, ptr, ...) @snprintf(ptr %buf, i64 1024, ptr @.lvk_fmt, ptr %sdk)
+  %h4 = call ptr @lvk_try(ptr %buf)
+  %n4 = icmp eq ptr %h4, null
+  br i1 %n4, label %fail, label %got4
+got4:
+  store ptr %h4, ptr @lvk_lib
+  br label %bind
+bind:
+  %n = call i32 @lvk_bind()
+  br label %ok
+ok:
+  ret i32 1
+fail:
+  ret i32 0
+}
+
+define ptr @lvk_sym(ptr %name) {
+entry:
+  %lib = load ptr, ptr @lvk_lib
+  %none = icmp eq ptr %lib, null
+  br i1 %none, label %no, label %look
+look:
+  %p = call ptr @dlsym(ptr %lib, ptr %name)
+  ret ptr %p
+no:
+  ret ptr null
+}
+
+define i32 @lvk_has(ptr %name) {
+entry:
+  %p = call ptr @lvk_sym(ptr %name)
+  %there = icmp ne ptr %p, null
+  %r = zext i1 %there to i32
+  ret i32 %r
+}