Driver: remove a stray s that propagated in cross-windows

The option is '--allow-multiple-definition' not '--allow-multiple-definitions'.

llvm-svn: 220760
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index fb2485d..d11fa4e 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -8254,7 +8254,7 @@
   }
 
   // NOTE: deal with multiple definitions on Windows (e.g. COMDAT)
-  CmdArgs.push_back("--allow-multiple-definitions");
+  CmdArgs.push_back("--allow-multiple-definition");
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());