Allow machine operands to represent global variables with offsets. This is

Allow machine operands to represent global variables with offsets.  This is
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!!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17007 91177308-0d34-0410-b5e6-96231b3b80d8