Index: COFF/CMakeLists.txt
===================================================================
--- COFF/CMakeLists.txt
+++ COFF/CMakeLists.txt
@@ -16,6 +16,7 @@
   ${LLVM_TARGETS_TO_BUILD}
   Core
   LTO
+  LibDriver
   MC
   MCDisassembler
   Support
Index: COFF/Driver.cpp
===================================================================
--- COFF/Driver.cpp
+++ COFF/Driver.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/LibDriver/LibDriver.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/Option.h"
@@ -185,6 +186,11 @@
   llvm::InitializeAllAsmPrinters();
   llvm::InitializeAllDisassemblers();
 
+  // If the first command line argument is "/lib", link.exe acts like lib.exe.
+  // We call our own implementation of lib.exe that understands bitcode files.
+  if (Argc > 1 && StringRef(Argv[1]).equals_lower("/lib"))
+    return llvm::libDriverMain(Argc - 1, Argv + 1) == 0;
+
   // Parse command line options.
   auto ArgsOrErr = Parser.parse(Argc, Argv);
   if (auto EC = ArgsOrErr.getError()) {