Report watchpoint hits during single stepping.

Summary:
Reorganized NativeProcessLinux::MonitorSIGTRAP to check for watchpoint hits on
TRAP_TRACE.

Added test for stepping over watchpoints.

https://llvm.org/bugs/show_bug.cgi?id=22814

Reviewers: ovyalov, tberghammer, vharron, clayborg

Subscribers: jingham, labath, lldb-commits

Differential Revision: http://reviews.llvm.org/D8404

llvm-svn: 232784