useful when you have a reference like:

int A[100];

void foo() { A[10] = 1; }

In this case, &A[10] is a single constant and should be treated as such.

Only MO_GlobalAddress and MO_ExternalSymbol are allowed to use this field, no
other operand type is.

This is another fine patch contributed by Jeff Cohen!!

llvm-svn: 17007