Change ConstantPoolSDNode to actually hold the Constant itself instead of

Change ConstantPoolSDNode to actually hold the Constant itself instead of
putting it into the constant pool.  This allows the isel machinery to
create constants that it will end up deciding are not needed, without them
ending up in the resultant function constant pool.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23081 91177308-0d34-0410-b5e6-96231b3b80d8