If we are trying to create a ConstantExpr cast that is really a GEP to the

If we are trying to create a ConstantExpr cast that is really a GEP to the
first element of an array, return a GEP instead of a cast.  This allows us
to transparently fold this:

int* getelementptr (int* cast ([100 x int]* %Gbody to int*), int 40)

into this:

int* getelementptr ([100 x int]* %Gbody, int 0, int 40)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16911 91177308-0d34-0410-b5e6-96231b3b80d8