Just create the file via 'touch'. This shouldn't break anything if the file happens to turn up at some point.
@@ -168,6 +168,9 @@ pathfix.py -i "%{__python3} %{py3_shbang_opts}" -p -n \
%build
+# Fix missing Makefile.rhelver
+touch Makefile.rhelver
+
# This ensures build-ids are unique to allow parallel debuginfo
perl -p -i -e "s/^CONFIG_BUILD_SALT.*/CONFIG_BUILD_SALT=\"%{kernel_name}\"/" .config