Align stubs for external and common global variables to pointer size.

This patch fixes PR36885: clang++ generates unaligned stub symbol
holding a pointer.

Patch by Rahul Chaudhry!

llvm-svn: 329030
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index da4244b..2926ea6 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1336,6 +1336,7 @@
       OutStreamer->SwitchSection(TLOF.getDataSection());
       const DataLayout &DL = M.getDataLayout();
 
+      EmitAlignment(Log2_32(DL.getPointerSize()));
       for (const auto &Stub : Stubs) {
         OutStreamer->EmitLabel(Stub.first);
         OutStreamer->EmitSymbolValue(Stub.second.getPointer(),