field into SubclassData in Value. This shrinks GlobalVAlue from 48->40
bytes, Function from 88->76, and GlobalVariable from 76->68. This trims
4640 bytes off my testcase, reading a bc file without materializing any
functions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36192 91177308-0d34-0410-b5e6-96231b3b80d8