GN: toolchain threading cleanup

tools/gn/ninja_script_target_writer.cc

Index: tools/gn/ninja_script_target_writer.cc
diff --git a/tools/gn/ninja_script_target_writer.cc b/tools/gn/ninja_script_target_writer.cc
index 1b8358cd79839f9ce948525c750acf1ef11e880e..e8cdef41933fd76682700443fa4c7bcfd9a162ce 100644
--- a/tools/gn/ninja_script_target_writer.cc
+++ b/tools/gn/ninja_script_target_writer.cc
@@ -11,8 +11,9 @@
 #include "tools/gn/target.h"
 
 NinjaScriptTargetWriter::NinjaScriptTargetWriter(const Target* target,
+                                                 const Toolchain* toolchain,
                                                  std::ostream& out)
-    : NinjaTargetWriter(target, out),
+    : NinjaTargetWriter(target, toolchain, out),
       path_output_no_escaping_(
           target->settings()->build_settings()->build_dir(),
           ESCAPE_NONE, false) {
@@ -152,7 +153,7 @@ void NinjaScriptTargetWriter::WriteStamp(
   out_ << "build ";
   path_output_.WriteFile(out_, helper_.GetTargetOutputFile(target_));
   out_ << ": "
-       << helper_.GetRulePrefix(target_->settings()->toolchain())
+       << helper_.GetRulePrefix(target_->settings())
        << "stamp";
   for (size_t i = 0; i < output_files.size(); i++) {
     out_ << " ";