(store_split_bit_field): If OP0 is a SUBREG, then compute WORD from the base register, instead of from the SUBREG.

(store_split_bit_field): If OP0 is a SUBREG, then
compute WORD from the base register, instead of from the SUBREG.
(extract_split_bit_field): Likewise.
(extract_bit_field): Sign-extend multiword bitfield if necessary.

From-SVN: r6668