For PR1205:

For PR1205:
Implement the first step towards arbitrary precision integer support in
LLVM. The APInt class provides arbitrary precision arithmetic and value
representation. This patch changes ConstantInt to use APInt as its value
representation without supporting bit widths > 64 yet. That change will
come after ConstantFolding handles bit widths > 64 bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34647 91177308-0d34-0410-b5e6-96231b3b80d8