[llvm] [flang] Don't associate pointers with zero sized storage targets (PR #155867)

[Eugene Epshteyn via llvm-commits]

eugeneepshteyn wrote:

> Please run the llvm-test-suite before merging; I think that GNU handles this case incorrectly and probably confirms it with a test; if so, it'll need to be disabled.

I did. These failures happen for me even without my change:
```
Failed Tests (2):
  test-suite :: Fortran/gfortran/regression/gfortran-regression-execute-regression__eoshift_bounds_1_f90.test
  test-suite :: Fortran/gfortran/regression/goacc/gfortran-regression-compile-regression__goacc__routine-3_f90.test
```
I think eoshift need to run at `-O0` and ACC test has issue generating LLVM module.

https://github.com/llvm/llvm-project/pull/155867