OnDiskHashTable: Use EndianStream.h to write little endian ostreams

Rather than rolling our own functions to write little endian data to
an ostream, we can use the support in llvm's EndianStream.h.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205044 91177308-0d34-0410-b5e6-96231b3b80d8
OnDiskHashTable: Use Endian.h to read little endian ostreams

Rather than rolling our own functions to read little endian data from
a buffer, we can use the support in llvm's Endian.h.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205045 91177308-0d34-0410-b5e6-96231b3b80d8