Issue 10344 Exiting _Dmain should flush all FILE*s and return nonzero on failure

Flushing all open streams on exit, throwing an Error with the errno string in case of failure.
Issue 10344 Exiting _Dmain should flush all FILE*s and return nonzero on failure

Moved to _d_run_main
Issue 10344 Exiting _Dmain should flush all FILE*s and return nonzero on failure

Don't show errno, just the strerror.
Merge branch 'fix10344' of github.com:lionello/druntime into fix10344