give MCAsmInfo a 'has little endian' bit. This is unfortunate, but

give MCAsmInfo a 'has little endian' bit.  This is unfortunate, but
I really want clients of the streamer to be able to say "emit this
64-bit integer" and have it get broken down right by the streamer.

I may change this in the future, we'll see how it works out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93934 91177308-0d34-0410-b5e6-96231b3b80d8