Fix test failure introduced in r187271 by enabling pipefail.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187381 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Replace the magic number with sizeof().

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187382 91177308-0d34-0410-b5e6-96231b3b80d8