Support script response files in GN.

tools/gn/substitution_writer.cc

Index: tools/gn/substitution_writer.cc
diff --git a/tools/gn/substitution_writer.cc b/tools/gn/substitution_writer.cc
index 0351eb17f97d0d981ff01c94943204fb4b843249..2af2e186e4be40504698f744a0b252ac35111f26 100644
--- a/tools/gn/substitution_writer.cc
+++ b/tools/gn/substitution_writer.cc
@@ -310,8 +310,10 @@ void SubstitutionWriter::WriteNinjaVariablesForSource(
     std::ostream& out) {
   for (const auto& type : types) {
     // Don't write SOURCE since that just maps to Ninja's $in variable, which
-    // is implicit in the rule.
-    if (type != SUBSTITUTION_SOURCE) {
+    // is implicit in the rule. RESPONSE_FILE_NAME is written separately
+    // only when writing target rules since it can never be used in any
+    // other context (like process_file_template).
+    if (type != SUBSTITUTION_SOURCE && type != SUBSTITUTION_RSP_FILE_NAME) {
       out << "  " << kSubstitutionNinjaNames[type] << " = ";
         EscapeStringToStream(
             out,