make tools dependant on llvm optional

FailStep.zig

@@ -0,0 +1,37 @@
+// This file implements a fail step for the build system
+// it's taken from Zig 0.14.0-dev and pasted here to be
+// used temporarily while we still target Zig 0.13.0
+const std = @import("std");
+const Step = std.Build.Step;
+const Fail = @This();
+
+step: Step,
+error_msg: []const u8,
+
+pub const base_id: Step.Id = .custom;
+
+pub fn create(owner: *std.Build, error_msg: []const u8) *Fail {
+    const fail = owner.allocator.create(Fail) catch @panic("OOM");
+
+    fail.* = .{
+        .step = Step.init(.{
+            .id = base_id,
+            .name = "fail",
+            .owner = owner,
+            .makeFn = make,
+        }),
+        .error_msg = owner.dupe(error_msg),
+    };
+
+    return fail;
+}
+
+fn make(step: *Step, prog_node: std.Progress.Node) !void {
+    _ = prog_node;
+
+    const fail: *Fail = @fieldParentPtr("step", step);
+
+    try step.result_error_msgs.append(step.owner.allocator, fail.error_msg);
+
+    return error.MakeFailed;
+}