Backport patch for increased rowhammer resistance from OpenBSD

[nmeum]

This commit backports an OpenBSD doas change which attempt to make doas more resistant to rowhammer attacks.

A similar change has been committed to sudo last year.

See:

• https://github.com/openbsd/src/commit/38599afa1d1d1f14a897b01350e8ce94486e1788
• https://github.com/sudo-project/sudo/commit/7873f8334c8d31031f8cfa83bd97ac6029309e4f
• https://doi.org/10.48550/arXiv.2309.02545