langref: disable an example that regressed from LLVM 14

doc/langref.html.in

@@ -9383,6 +9383,12 @@ const std = @import("std");
 const expect = std.testing.expect;
 
 test "vector @reduce" {
+    // This test regressed with LLVM 14:
+    // https://github.com/llvm/llvm-project/issues/55522
+    // We'll skip this test unless the self-hosted compiler is being used.
+    // After LLVM 15 is released we can delete this line.
+    if (@import("builtin").zig_backend == .stage1) return;
+
     const value = @Vector(4, i32){ 1, -1, 1, -1 };
     const result = value > @splat(4, @as(i32, 0));
     // result is { true, false, true, false };