[XRay] Make the FDRTraceWriter Endian-aware

Before this patch, the FDRTraceWriter would not take endianness into
account when writing data into the output stream.

This is a follow-up to D51289 and D51210.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341223 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed