Allow the bootstrap binary of GN (the one in TEMPDIR) to build and run on FreeBSD.

tools/gn/args.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/args.h"
 
 #include "build/build_config.h"
 #include "tools/gn/variables.h"
 
 #if defined(OS_WIN)
@@ skipping 191 matching lines @@
   lock_.AssertAcquired();
 
   // Host OS.
   const char* os = NULL;
 #if defined(OS_WIN)
   os = "win";
 #elif defined(OS_MACOSX)
   os = "mac";
 #elif defined(OS_LINUX)
   os = "linux";
+#elif defined(OS_FREEBSD)
+  os = "freebsd";
 #else
   #error Unknown OS type.
 #endif
   Value os_val(NULL, std::string(os));
   dest->SetValue(variables::kBuildOs, os_val, NULL);
   dest->SetValue(variables::kOs, os_val, NULL);
 
   // Host architecture.
   static const char kX86[] = "x86";
   static const char kX64[] = "x64";
@@ skipping 56 matching lines @@
        i != values.end(); ++i)
     scope->SetValue(i->first, i->second, i->second.origin());
 }
 
 void Args::SaveOverrideRecordLocked(const Scope::KeyValueMap& values) const {
   lock_.AssertAcquired();
   for (Scope::KeyValueMap::const_iterator i = values.begin();
        i != values.end(); ++i)
     all_overrides_[i->first] = i->second;
 }