Make sure that if anyone passes a name by accident for the isSigned

Make sure that if anyone passes a name by accident for the isSigned
parameter of CreateIntCast then they get an error from the compiler
(or from the linker with a non-gcc compiler).  Another possibility
is to flip the order of the DestTy and isSigned parameters, since you
should then get a compiler warning if you try to use a char* for a
Type*.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88913 91177308-0d34-0410-b5e6-96231b3b80d8