[Samba] samba-4.12.3 RPM building tools for RHEL 7 and 8

[Nico Kadel-Garcia]

I've updated the hooks I publish for building samba to include 4.12.3
they're at:

    https://github.com/nkadel/samba4repo

It's updated from the Fedora rawhide .spec file, which provides a new
"samba-winexe" package. That package cannot be built for RHEL 7,
because EPEL no longer publishes mingw32 and mingw64 packages for RHEL
7. Not only no longer publishes them, but withdrew them from the
public repositories and the archive repositories.

It also includes updating the libldb hooks to 2.1.3.