Build FreeBSD as a Linux variant in GN (series 0003): is_linux and
is_clang are true for current_os "freebsd", matching the C++ side,
where __FreeBSD__ already selects DART_HOST_OS_LINUX.
FreeBSD-specific, not submitted upstream yet.
--- build/config/BUILDCONFIG.gn.orig	2026-09-29 08:00:52 UTC
+++ build/config/BUILDCONFIG.gn
@@ -117,7 +117,8 @@ declare_args() {
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
-  is_clang = current_os == "mac" || current_os == "linux"
+  is_clang = current_os == "mac" || current_os == "linux" ||
+             current_os == "freebsd"
 
   # Compile for Address Sanitizer to find memory bugs.
   is_asan = false
@@ -201,7 +202,10 @@ if (current_os == "win") {
   is_posix = true
   is_watchos = false
   is_win = false
-} else if (current_os == "linux") {
+} else if (current_os == "linux" || current_os == "freebsd") {
+  # FreeBSD is built as a variant of Linux, matching the C++ side where
+  # __FreeBSD__ selects DART_HOST_OS_LINUX (see runtime/platform/globals.h).
+  # Use current_os == "freebsd" where the two differ.
   is_android = false
   is_chromeos = false
   is_fuchsia = false