feature/logtail: pull logtail + netlog out to modular features

Removes 434 KB from the minimal Linux binary, or ~3%.

Primarily this comes from not linking in the zstd encoding code.

Fixes #17323

Change-Id: I0a90de307dfa1ad7422db7aa8b1b46c782bfaaf7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_logtail_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_logtail
+
+package buildfeatures
+
+// HasLogTail is whether the binary was built with support for modular feature "upload logs to log.tailscale.com (debug logs for bug reports and also by network flow logs if enabled)".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_logtail" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasLogTail = false

feature/buildfeatures/feature_logtail_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_logtail
+
+package buildfeatures
+
+// HasLogTail is whether the binary was built with support for modular feature "upload logs to log.tailscale.com (debug logs for bug reports and also by network flow logs if enabled)".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_logtail" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasLogTail = true

feature/buildfeatures/feature_netlog_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_netlog
+
+package buildfeatures
+
+// HasNetLog is whether the binary was built with support for modular feature "Network flow logging support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_netlog" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasNetLog = false

feature/buildfeatures/feature_netlog_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_netlog
+
+package buildfeatures
+
+// HasNetLog is whether the binary was built with support for modular feature "Network flow logging support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_netlog" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasNetLog = true