Fix file creation on OpenBSD

[horrad]

On OpenBSD at least one of O_RDONLY, O_WRONLY or O_RDWR is needed to open a file.

In creating a new file none of those is set, which leads to an EINVAL error ("invalid argument").

Since the new file is only created and never read, I chose to use O_WRONLY.

[N-R-K]

@horrad Please put what you wrote in the PR description in the commit message body as well.

[horrad]

@horrad Please put what you wrote in the PR description in the commit message body as well.
Done.

[jarun]

Can you please make the patch BSD-specific?

[KlzXS]

I think it's best we avoid adding unnecessary #ifdefs. open(2) says:

The argument flags must include one of the following access
modes: O_RDONLY, O_WRONLY, or O_RDWR.

We have none of those.

[jarun]

Makes sense. Merged. Thanks!