* linux-low.h (struct lwp_info): New fields
`stopped_by_watchpoint' and `stopped_data_address'.
* linux-low.c (linux_wait_for_lwp): Check for watchpoint triggers
here, and cache them in the lwp object.
(wait_for_sigstop): Check stopped_by_watchpoint lwp field
directly.
(linux_resume_one_lwp): Clear the lwp's stopped_by_watchpoint
field.
(linux_stopped_by_watchpoint): Rewrite.
(linux_stopped_data_address): Rewrite.