main/busybox: include fixes for sed regex delimiter parsing
Similar to the awk fix, which also isn't upstream yet and was backported from the ML, this can cause subtle hard-to-debug breakage in software buildsystems which make use of sed(1). Hence, it's useful to include it even if isn't upstream yet.
See: https://lists.busybox.net/pipermail/busybox/2024-November/091023.html