Build FreeBSD as a Linux variant in GN (series 0003): take the Linux
branches of the runtime configs for target_os "freebsd".
FreeBSD-specific, not submitted upstream yet.
--- runtime/BUILD.gn.orig	2026-09-29 08:00:52 UTC
+++ runtime/BUILD.gn
@@ -31,7 +31,7 @@ config("dart_maybe_product_config") {
     }
     assert(!dart_debug)
     defines += [ "PRODUCT" ]
-    if (target_os == "linux") {
+    if (target_os == "linux" || target_os == "freebsd") {
       defines += [ "DART_DISABLE_TIMELINE" ]
     }
   }
@@ -44,7 +44,8 @@ config("dart_product_config") {
   cflags = []
   if (!dart_debug) {
     defines += [ "PRODUCT" ]
-    if (dart_runtime_mode == "release" && target_os == "linux") {
+    if (dart_runtime_mode == "release" &&
+        (target_os == "linux" || target_os == "freebsd")) {
       defines += [ "DART_DISABLE_TIMELINE" ]
     }
   }
@@ -125,7 +126,8 @@ config("dart_os_config") {
     # If we need to differentiate iOS and watchOS targets later, we'll
     # change this.
     defines += [ "DART_TARGET_OS_MACOS_IOS" ]
-  } else if (target_os == "linux") {
+  } else if (target_os == "linux" || target_os == "freebsd") {
+    # FreeBSD is a Linux variant, see //build/config/BUILDCONFIG.gn.
     defines += [ "DART_TARGET_OS_LINUX" ]
   } else if (target_os == "mac") {
     defines += [ "DART_TARGET_OS_MACOS" ]