GN: toolchain threading cleanup

tools/gn/ninja_helper.h

Index: tools/gn/ninja_helper.h
diff --git a/tools/gn/ninja_helper.h b/tools/gn/ninja_helper.h
index bef2fcd55538ac0ff9baec89f02fe3a3532b4965..84a2c896302976cce7e3eb880f6778a01e5ed329 100644
--- a/tools/gn/ninja_helper.h
+++ b/tools/gn/ninja_helper.h
@@ -52,12 +52,11 @@ class NinjaHelper {
 
   // Returns the prefix for rules on the given toolchain. We need this to
   // disambiguate a given rule for each toolchain.
-  std::string GetRulePrefix(const Toolchain* toolchain) const;
+  std::string GetRulePrefix(const Settings* settings) const;
 
   // Returns the name of the rule name for the given toolchain and file/target
   // type.  Returns the empty string for source files with no command.
   std::string GetRuleForSourceType(const Settings* settings,
-                                   const Toolchain* toolchain,
                                    SourceFileType type) const;
 
   // Returns the relative directory in either slashes or the system separator