comptime VM arc: abi(.compiler) ABI, out as sx fn, VM-native diagnostics, BuildConfig threaded

Lands the full VM/compiler-API arc on branch reify (701/0 both gates):
- abi(.compiler) ABI replaces abi(.zig) extern compiler + the fake
  #library "compiler"; bodiless decl = compiler-API surface, bodied =
  user compiler-domain fn (lowered for VM eval, emit-skipped).
- out is a plain sx fn (libc write) — the out builtin deleted; the VM
  handles it via host-FFI. trace_resolve + interp_print_frames ported.
- 4B VM-native diagnostics: 1179/1180 render proper comptime type
  construction failed: under strict.
- S5a: build_options/set_post_link_callback on abi(.compiler) with
  BuildConfig threaded into the VM (green intermediate).
- 0522 fixed (describe(args: []Type)); regression 0638.

Strict deletion-gate down to 4 compiler_call bails (1609/1614/1615/1616)
+ 1654 (legitimate unresolvable-symbol diagnostic).

src/ir/lower/call.zig

@@ -1296,8 +1296,8 @@ pub fn resolveFuncByName(self: *Lowering, name: []const u8) ?FuncId {
 
 pub fn resolveBuiltin(name: []const u8) ?inst_mod.BuiltinId {
     const builtins = .{
-        // Note: "print" is NOT here — it's a comptime-expanded function, not a simple builtin
-        .{ "out", inst_mod.BuiltinId.out },
+        // Note: "print" is NOT here — it's a comptime-expanded function, not a simple builtin.
+        // "out" is NOT here either — it's a plain sx function (libc `write`), not a builtin.
         .{ "sqrt", inst_mod.BuiltinId.sqrt },
         .{ "sin", inst_mod.BuiltinId.sin },
         .{ "cos", inst_mod.BuiltinId.cos },