Mark ForEachMacros as iterator names

Mark ForEachMacros as iterator names

After f10f5572ac7e0520eed4516be52df625ad56c860 spatch started reporting
the following warnings:

    Impossible: How can diff be null and have not Correct in compare_c? Tag1 ("diff token: ( VS (\nFile \"./lib/dns/include/dns/rdatasetiter.h\", line 109, column 32, charpos = 3103\n  around = '(',\n  whole content = #define DNS_RDATASETITER_FOREACH(rds)               \\\nFile \"/tmp/cocci-output-110376-c54da3-rdatasetiter.h\", line 109, column 32, charpos = 3103\n  around = '(',\n  whole content = #define DNS_RDATASETITER_FOREACH(rds)               \\\n")
    Impossible: How can diff be null and have not Correct in compare_c? Tag1 ("diff token: ( VS (\nFile \"./lib/dns/include/dns/dbiterator.h\", line 114, column 30, charpos = 3413\n  around = '(',\n  whole content = #define DNS_DBITERATOR_FOREACH(rds)               \\\nFile \"/tmp/cocci-output-110387-883f2f-dbiterator.h\", line 114, column 30, charpos = 3413\n  around = '(',\n  whole content = #define DNS_DBITERATOR_FOREACH(rds)               \\\n")

See https://github.com/coccinelle/coccinelle/issues/398.