* proc/native/linux: only set breakpoints on threads that receive SIGTRAP
* proc/native/linux: do not call (*Thread).Stopped inside (*Process).stop
(*Thread).Stopped is slow because it needs to open, read and parse a
file in /proc, we don't actually need to do that, we can just rely on
the value of Thread.os.running.
Benchmark before:
BenchmarkConditionalBreakpoints-4 1 12476166303 ns/op
Benchmark after:
BenchmarkConditionalBreakpoints-4 1 10403533675 ns/op
Conditional breakpoint evaluation: 1.24ms -> 1ms
Updates #1549
e9b2da17cb