Add some patterns for globals, so we can now compile this:

static unsigned long long X, Y;
void test1() {
  X = Y;
}

into:

_test1:
        lis r2, ha16(_Y)
        lis r3, ha16(_X)
        ld r2, lo16(_Y)(r2)
        std r2, lo16(_X)(r3)
        blr

llvm-svn: 28879