ADT: Add SmallVector<>::emplace_back(): fixup

Add missing `void` return type from `!LLVM_HAS_VARIADIC_TEMPLATES` case
in r223201.

llvm-svn: 223202
diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index 8c29f5c..1ba9c41 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -246,7 +246,7 @@
   }
 #else
 private:
-  template <typename Constructor> emplace_back_impl(Constructor emplace) {
+  template <typename Constructor> void emplace_back_impl(Constructor emplace) {
     if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
       this->grow();
     emplace((void *)this->end());