Allow bytecode files to refer directly to global values as constants, instead

Allow bytecode files to refer directly to global values as constants, instead
of forcing them to go through ConstantPointerRef's.  This allows bytecode
files to mirror .ll files, allows more efficient encoding, and makes it easier
to eventually eliminate CPR's.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10883 91177308-0d34-0410-b5e6-96231b3b80d8