Build fails on macOS because of sed error

It appears the build system for Pike assumes the user is using GNU sed, and the build will fail on macOS (and likely other BSD-based systems) with this error:

sed: RE error: illegal byte sequence

This can be resolved by making sure that all invocations of sed in the build system are compatible with both GNU and BSD sed, or by checking early in the configure script for GNU sed and explicitly failing if a compatible sed is not found.