Add .note.GNU-stack section to produced executables (llvm#162)

Do this unconditionally because there's no scenario where we would need executable stack for managed code.

llvm/tools/objwriter/objwriter.cpp

@@ -147,6 +147,7 @@ bool ObjectWriter::Init(llvm::StringRef ObjectFilePath, const char* tripleName)
       /*DWARFMustBeAtTheEnd*/ false);
   if (!Streamer)
     return error("no object streamer for target " + TripleName);
+  Streamer->InitSections(/* NoExecStack */ true);
   Assembler = &Streamer->getAssembler();
 
   FrameOpened = false;