gn: Support build directories outside the source tree.

tools/gn/target_generator.cc

Index: tools/gn/target_generator.cc
diff --git a/tools/gn/target_generator.cc b/tools/gn/target_generator.cc
index 975ff722414da3881ae401c05028fce1db92fbc5..c61f7f2d5defbd6c948c246c3a370432b1d44139 100644
--- a/tools/gn/target_generator.cc
+++ b/tools/gn/target_generator.cc
@@ -318,7 +318,8 @@ bool TargetGenerator::FillGenericConfigs(const char* var_name,
                                          UniqueVector<LabelConfigPair>* dest) {
   const Value* value = scope_->GetValue(var_name, true);
   if (value) {
-    ExtractListOfUniqueLabels(*value, scope_->GetSourceDir(),
+    ExtractListOfUniqueLabels(scope_->settings()->build_settings(),
+                              *value, scope_->GetSourceDir(),
                               ToolchainLabelForScope(scope_), dest, err_);
   }
   return !err_->has_error();
@@ -328,7 +329,8 @@ bool TargetGenerator::FillGenericDeps(const char* var_name,
                                       LabelTargetVector* dest) {
   const Value* value = scope_->GetValue(var_name, true);
   if (value) {
-    ExtractListOfLabels(*value, scope_->GetSourceDir(),
+    ExtractListOfLabels(scope_->settings()->build_settings(),
+                        *value, scope_->GetSourceDir(),
                         ToolchainLabelForScope(scope_), dest, err_);
   }
   return !err_->has_error();
@@ -338,7 +340,8 @@ bool TargetGenerator::FillForwardDependentConfigs() {
   const Value* value = scope_->GetValue(
       variables::kForwardDependentConfigsFrom, true);
   if (value) {
-    ExtractListOfUniqueLabels(*value, scope_->GetSourceDir(),
+    ExtractListOfUniqueLabels(scope_->settings()->build_settings(),
+                              *value, scope_->GetSourceDir(),
                               ToolchainLabelForScope(scope_),
                               &target_->forward_dependent_configs(), err_);
   }