Analyse following RPM build log snippet. Describe contents accurately, without speculation or suggestions for resolution.            
Your analysis must be as concise as possible, while keeping relevant information intact.
Snippet: 
Checking for unpackaged file(s): /usr/lib/rpm/check-files /builddir/build/BUILD/fwupd-2.0.8-build/BUILDROOT
error: Installed (but unpackaged) file(s) found:
   /etc/grub.d/35_fwupd
RPM build errors:
    Installed (but unpackaged) file(s) found:
   /etc/grub.d/35_fwupd
RPM complains about unpackaged files.