Fix CentOS 8 builds

Apparently something has changed upstream and openSUSE has not yet
tracked this in their prjconf, added here meanwhile

mpcdf_common.py

@@ -61,6 +61,7 @@ def dist_prjconf_tags(distribution):
 
     centos8_prjconf_tags = textwrap.dedent(
         """
+        Preinstall: libzstd
         ExpandFlags: module:python36-3.6
         # Remove redhat-hardened-cc1 and redhat-annobin-cc1 spec
         Optflags: x86_64 -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -m64 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection