doctor: add ts_omit_doctor support

Updates #12614

Change-Id: I84c166c4b99ca75d70abe4087e5ff3f7d90d4bcc
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_doctor_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_doctor
+
+package buildfeatures
+
+// HasDoctor is whether the binary was built with support for modular feature "Diagnose possible issues with Tailscale and its host environment".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_doctor" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasDoctor = false

feature/buildfeatures/feature_doctor_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_doctor
+
+package buildfeatures
+
+// HasDoctor is whether the binary was built with support for modular feature "Diagnose possible issues with Tailscale and its host environment".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_doctor" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasDoctor = true