* dwarf2-frame.h (enum dwarf2_frame_reg_rule): Add

* dwarf2-frame.h (enum dwarf2_frame_reg_rule): Add
DWARF2_FRAME_REG_SAVED_VAL_OFFSET and
DWARF2_FRAME_REG_SAVED_VAL_EXP.
* dwarf2-frame.c (execute_cfa_program): Handle val_offset,
val_offset_sf and val_expression.
(dwarf2_frame_prev_register): Handle the new reg rules.
(dwarf2_frame_this_id): Use pc instead of function entry point.