[llvm] [Flang] [Runtime ]Fix write endfile abort (PR #191633)

[via llvm-commits]

kwyatt-ext wrote:

I verified that Flang's behavior related to READ is fine.  The standard implies that it is processor dependent, so considering it a EOF error is ok.  I also verified that the 2 paths removed related to BeginExternalFormattedIO() and BeginExternalListIO() did not exhibit the same error behavior.

https://github.com/llvm/llvm-project/pull/191633