--- a/v8/BUILD.gn
+++ b/v8/BUILD.gn
@@ -59,6 +59,13 @@
   v8_metagen_libclang_so = ""
   v8_metagen_libclang_bindings_dir = ""
 
+  # Override for the clang resource dir (the dir holding
+  # include/{stddef.h,stdarg.h,...}). Defaults to
+  # "$clang_base_path/lib/clang/$clang_version", which assumes the bundled
+  # toolchain layout. Distros whose clang installs its resource dir
+  # elsewhere (e.g. Gentoo) can point this at their own resource dir.
+  v8_metagen_clang_resource_dir = ""
+
   # Dynamically set an additional dependency from v8/custom_deps.
   v8_custom_deps = ""
 
@@ -2485,7 +2492,11 @@
 
   # The clang toolchain's resource dir contains builting headers
   # include/{stddef.h,stdarg.h,...}.
-  _metagen_clang_resource_dir = "$clang_base_path/lib/clang/$clang_version"
+  if (v8_metagen_clang_resource_dir == "") {
+    _metagen_clang_resource_dir = "$clang_base_path/lib/clang/$clang_version"
+  } else {
+    _metagen_clang_resource_dir = v8_metagen_clang_resource_dir
+  }
   _metagen_flags_target = ":v8_base_without_compiler"
   _metagen_flags_target_ninja =
       get_label_info(_metagen_flags_target, "target_out_dir") +