Fix msan buildbot.

This patch should fix sanitizer-x86_64-linux-fast bot.

The problem was that the contents of this stream are aligned to 4 byte,
and the paddings were created just by incrementing `Offset`, so paddings
had undefined values. When the entire stream is written to an output,
it triggered msan.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305541 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed