Set prefix variable in MAKE_FLAGS so that the *.pc files use the
correct paths.
Use gsed tool since -i flag is used during build.
Disable Go library.
Skip portability check of contrib/pcaps4server; it is not installed
or used during build.
Upstream release notes:
https://sites.google.com/site/fullycapable/release-notes-for-libcap#h.bkhhw1fow1su