Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -8718,6 +8718,9 @@
     }
   }
 
+  // No need to do anything for pthreads. Claim argument to avoid warning.
+  Args.ClaimAllArgs(options::OPT_pthread);
+
   const char *Exec = Args.MakeArgString(getToolChain().GetLinkerPath());
   std::unique_ptr<Command> Cmd =
       llvm::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs);
Index: test/Driver/darwin-ld-pthread.c
===================================================================
--- /dev/null
+++ test/Driver/darwin-ld-pthread.c
@@ -0,0 +1,5 @@
+// RUN: %clang -target x86_64-apple-darwin -c -o %t.o %s
+// RUN: %clang -Wunused-command-line-argument -pthread -target x86_64-apple-darwin -### %t.o -o %t.bin 2>&1 | FileCheck %s
+
+// There is nothing to do at link time to get pthread support. But do not warn.
+// CHECK-NOT: argument unused during compilation: '-pthread'