Use llvm::sys::IsBigEndianHost.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179529 91177308-0d34-0410-b5e6-96231b3b80d8
Fix unused variable warning with assertions disabled.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179531 91177308-0d34-0410-b5e6-96231b3b80d8