configure: add --enable-rpm415 option

configure: add --enable-rpm415 option

It's useful to be able to force the build system into avoiding the use
of rpm 4.15 version or higher.  That version of RPM is the one that
supports RPMs from Fedora 31 or higher.  Those RPMs use the zstd
compression scheme.  Prior to Fedora 31, RPM were not using the zstd
compression scheme.  So, systems with rpm version lower than 4.15
cannot deal with RPMs coming from Fedora 31 or higher.  So on those
systems, some regression tests of libabigail who use RPMs from Fedora
33 will fail.

With this patch, one can use the --disable-rpm415 option of the
configure script to prevent those tests from running on those pre 4.15
rpm systems.

	* configure: Introduce the --{en, dis}able-rpm415 option.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>