This change fixes the ExponentialGrowthAppendingBinaryByteStream
tests on big endian machines.
Force ExponentialGrowthAppendingBinaryByteStreams to use little-
endian byte order. We always used little-endian byte order anyway
and it seems very unlikely we'll need the flexibility to make the
stream big-endian in the future. The benefit of this is that we
can use portable APIs while still allowing the compiler to remove
conditional byte swaps.
Also replace writeRaw with writeInteger and make it explicitly
little-endian to make the API cleaner and more portable.
If we know the size of a type at compile time (like we do for all the
integer types), it is cheaper to assign the data buffer directly instead
of using a memcpy.
It is more efficient than llvm::AppendingBinaryByteStream if a lot of
small data gets appended to it because it doesn't need to resize its
buffer on each write.
