feature/ace: make ACE modular

Updates #12614

Change-Id: Iaee75d8831c4ba5c9705d7877bb78044424c6da1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_ace_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_ace
+
+package buildfeatures
+
+// HasACE is whether the binary was built with support for modular feature "Alternate Connectivity Endpoints".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_ace" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasACE = false

feature/buildfeatures/feature_ace_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_ace
+
+package buildfeatures
+
+// HasACE is whether the binary was built with support for modular feature "Alternate Connectivity Endpoints".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_ace" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasACE = true