Previously it would accept anything matching /clean$/. Now we check for the 4
names that we know the top level Makefile defines.
if ($target eq '') {
die "make_ext: no make target specified (eg all or clean)\n";
-} elsif ($target !~ /(?:^all|clean)$/) {
+} elsif ($target !~ /^(?:all|clean|distclean|realclean|veryclean)$/) {
# for the time being we are strict about what make_ext is used for
die "$0: unknown make target '$target'\n";
}