Add sparsehash-devel in CRB
sparsehash-devel used to be in CentOS 8 Powertools
Add it to CRB.
The package does seem to be built.
https://kojihub.stream.centos.org/koji/buildinfo?buildID=6832
This may have impact on https://bugzilla.redhat.com/show_bug.cgi?id=2047208 which is an EPEL request for the package.