I ran a database query and it looks like GPL was found in these files:
compilers/imcc/imcparser.c compilers/imcc/imcparser.h compilers/pirc/macro/macroparser.c compilers/pirc/macro/macroparser.h compilers/pirc/new/pirparser.c compilers/pirc/new/pirparser.h languages/cola/parser.c languages/cola/parser.h languages/plumhead/src/yacc/plumhead_parser.c languages/plumhead/src/yacc/plumhead_parser.h
Artistic turned up here:
From a casual glance, it looks like the GPL citations are false positives caused by Bison. This was discussed previously in this thread. Our license parser isn't smart enough to recognize that GPL doesn't apply when you are using Bison in this way, so there will need to be some work on our end to make these licensing flags go away.