* i386-tdep.c (i386_frameless_signal_p): New function.

* i386-tdep.c (i386_frameless_signal_p): New function.
(i386_frame_chain): Deal with frameless signals.
(i386_sigtramp_saved_sp): New function.
(i386_frame_saved_pc): Deal with frameless signals.
(i386_saved_pc_after_call): Make sure the correct value is
returned just after entry into a sigtramp.
* i386bsd-tdep.c (i386bsd_sc_sp_offset, i386nbsd_sc_sp_offset,
i386fbsd4_sc_sp_offset): New variables.
(i386bsd_init_abi, i386nbsd_init_abi, i386fbsd4_init_abi): Use
these variables to initialize tdep->sc_sp_offset.  * i386bsd-nat.c
(_initialize_i386bsd_nat): Add sanity check for sc_sp_offset
similiar to what we already did for sc_pc_offset.
* i386-sol2-tdep.c (i386_sol2_init_abi): Initialize
tdep->sc_sp_offset.