Fix driver warning about -pthread on Android.

-pthread is no-op on Android. Suppress the unused argument warning.

llvm-svn: 210253
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 7817f82..37df7ee 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -7189,9 +7189,9 @@
       }
       AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
 
-      if (!isAndroid &&
-          (Args.hasArg(options::OPT_pthread) ||
-           Args.hasArg(options::OPT_pthreads) || UsedOpenMPLib != LibUnknown))
+      if ((Args.hasArg(options::OPT_pthread) ||
+           Args.hasArg(options::OPT_pthreads) || UsedOpenMPLib != LibUnknown) &&
+          !isAndroid)
         CmdArgs.push_back("-lpthread");
 
       CmdArgs.push_back("-lc");