[PATCH] Add function for consuming endian specific data from a buffer

[Rafael Espíndola]

> I'm not aware of any uses of input streams in LLVM. Generally, I expect
> this to be used on MemoryBuffers, and some of the uses I updated in
> clang read from StringRefs in this way.

OK. It might be worth it to try to "read" a larger structure at a time
like we do for lib/Object, but this function is probably fine for now.

Cheers,
Rafael