portability fixes: support building vboot on OpenBSD This was done on OpenBSD 6.8. Required packages are: e2fsprogs and gcc. Change-Id: I86ec080e1ddb90053d81f1edd17d3406e7e737c6 Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2903352 Reviewed-by: Patrick Georgi <[email protected]> Tested-by: Patrick Georgi <[email protected]> Commit-Queue: Patrick Georgi <[email protected]>