PNaCl: Strip `nonnull` attributes from pointer arguments.

lib/Transforms/NaCl/ReplacePtrsWithInts.cpp

Index: lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
diff --git a/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp b/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
index d1d2d179365dcb86138f0a52ee001a07800746ad..88bc10e1df9f8ce85e1433a5b257747e6c1efaac 100644
--- a/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
+++ b/lib/Transforms/NaCl/ReplacePtrsWithInts.cpp
@@ -331,6 +331,7 @@ static AttributeSet RemovePointerAttrs(LLVMContext &Context,
         case Attribute::NoAlias:
         case Attribute::ReadNone:
         case Attribute::ReadOnly:
+        case Attribute::NonNull:
           break;
         default:
           AB.addAttribute(*Attr);