Index: lib/Core/Reproduce.cpp
===================================================================
--- lib/Core/Reproduce.cpp
+++ lib/Core/Reproduce.cpp
@@ -93,6 +93,7 @@
     Res = Root.substr(2);
 
   path::append(Res, path::relative_path(Abs));
+  std::replace(Res.begin(), Res.end(), '\\', '/');
 
   return Res.str();
 }
Index: test/ELF/reproduce-windows2.s
===================================================================
--- test/ELF/reproduce-windows2.s
+++ test/ELF/reproduce-windows2.s
@@ -0,0 +1,11 @@
+# REQUIRES: x86, cpio
+
+# Test that a response.txt file always uses / instead of \.
+# RUN: rm -rf %t.dir
+# RUN: mkdir -p %t.dir/build
+# RUN: llvm-mc %s -o %t.dir/build/foo.o -filetype=obj -triple=x86_64-pc-linux
+# RUN: cd %t.dir
+# RUN: ld.lld build/foo.o --reproduce repro
+# RUN: echo "*response.txt" > list.txt
+# RUN: cpio -i --to-stdout --pattern-file=list.txt < repro.cpio | FileCheck %s
+# CHECK: {{.*}}/build/foo.o