Bison Exp doesn't compile

[Akim Demaille]

Please, address the warnings (i.e., configure with
--enable-gcc-warnings):

gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I. -I../src -I../intl    -g -O2 -Wall -W 
-Wbad-function-cast -Wcast-align -Wcast-qual -Wformat -Wmissing-declarations 
-Wmissing-prototypes -Wnested-externs -Wshadow -Wstrict-prototypes 
-Wwrite-strings -Werror -c `test -f hash.c || echo './'`hash.c
cc1: warnings being treated as errors
hash.c: In function `hash_insert_at':
hash.c:133: warning: cast discards qualifiers from pointer target type
hash.c: In function `hash_delete_at':
hash.c:155: warning: cast discards qualifiers from pointer target type