rpm (4.11) is complaining about:
extracting debug info from /builddir/build/BUILDROOT/zstd-1.5.6-1.el7.x86_64/usr/lib64/libzstd.so.1.5.6
/usr/lib/rpm/debugedit: canonicalization unexpectedly shrank by one character
This was only addressed in rpm >= 4.13,
so lets avoid the double slash hunt as described in:
https://bugzilla.redhat.com/show_bug.cgi?id=304121
We can address if a newer zstd is explicitly requested for centos 7