[llvm] [flang][runtime] OPEN(existingUnit,POSITION=) (PR #153688)

[Peter Klausler via llvm-commits]

klausler wrote:

> LGTM. Any tests possible?

Best left to end-to-end Fortran testing, which isn't really possible in llvm-project.  Maybe @danielcchen has plans to contribute these tests to llvm-test-suite?

https://github.com/llvm/llvm-project/pull/153688