PNaCl: Fix handling of va_arg on structs in simplification passes

lib/Transforms/NaCl/ExpandVarArgs.cpp

Index: lib/Transforms/NaCl/ExpandVarArgs.cpp
diff --git a/lib/Transforms/NaCl/ExpandVarArgs.cpp b/lib/Transforms/NaCl/ExpandVarArgs.cpp
index 0fd1a3cb44f1f11096e457ce964c22c7e8d20ee3..f4f82adf66993f026d38b782f6bd31c7323cd3a9 100644
--- a/lib/Transforms/NaCl/ExpandVarArgs.cpp
+++ b/lib/Transforms/NaCl/ExpandVarArgs.cpp
@@ -17,21 +17,15 @@
 // Alignment:
 //
 // This pass does not add any alignment padding between the arguments
-// that are copied onto the stack.  We assume that the only argument
-// types that need to be handled are 32-bit and 64-bit -- i32, i64,
-// pointers and double:
+// that are copied onto the stack.  This means that if the argument
+// list contains a mixture of, say, 1-byte and 4-byte values, the code
+// generated by this pass might be inefficient due to the memory
+// accesses being unaligned.
 //
-//  * We won't see i1, i8, i16 and float as varargs arguments because
-//    the C standard requires the compiler to promote these to the
-//    types "int" and "double".
-//
-//  * We won't see va_arg instructions of struct type because Clang
-//    does not yet support them in PNaCl mode.  See
-//    https://code.google.com/p/nativeclient/issues/detail?id=2381
-//
-// If such arguments do appear in the input, this pass will generate
-// correct, working code, but this code might be inefficient due to
-// using unaligned memory accesses.
+// This should only be an issue when passing structs as varargs
+// arguments.  We won't see i1, i8, i16 and float as varargs arguments
+// because the C standard requires the compiler to promote these to
+// the types "int" and "double".
 //
 //===----------------------------------------------------------------------===//