Flang accepts -module-dir as short-style option

f820625503744472be8312bb70ee0da197816067 claims that gfortran would treat `-module-dir` exactly like `-J`. This is not thee case:

```
$ gfortran -J/home/meinersbur/finclude
gfortran: fatal error: no input files
$ gfortran -module-dir/home/meinersbur/finclude
gfortran: error: unrecognized command-line option ‘-module-dir/home/meinersbur/finclude’
```

But flang accepts both:
```
$ flang -J/home/meinersbur/finclude
flang-22: error: no input files
$ gfortran -module-dir/home/meinersbur/finclude
flang-22: error: no input files
```

Flang is confusing short- and long-format command line arguments. The way to pass argument to long-style option is one of:
```
$ flang -module-dir=/home/meinersbur/finclude
flang-22: error: no input files
$ flang -module-dir /home/meinersbur/finclude
flang-22: error: no input files
```
The consequence is that if flang would introduce a new option such as `-module-directives`, it could not be distiguished from `-module-dir=ectives`.