Add support for reading bytecode files with compactiontables for bytecode files.

Add support for reading bytecode files with compactiontables for bytecode files.
This shrinks the bytecode file for 176.gcc by about 200K (10%), and 254.gap by
about 167K, a 25% reduction.  There is still a lot of room for improvement in
the encoding of the compaction table.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10914 91177308-0d34-0410-b5e6-96231b3b80d8