[OSX][Legacy runtime] Editor crashes after attaching VS debugger few times

1. What happened
Similar to case 941204, but with the old runtime. Also, you have to click Start/Stop debugging button much faster, like 3-4 times/second.

2. How we can reproduce it using the example you attached
- Attached is an empty project with 1 default script.
- Open script in VS
- Start clicking 'Play'/'Stop' debugger btn in VS to attach/detach debugger very fast
- Continue for a few seconds
>>> Crash.
Usually, only OSX crash reporter is invoked, but this time Unity Bug Reporter was launched as well.

Editor log ends with:
=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================

This is reproducible in 2017.3.0a7, 2017.2.0b11, 2017.1.1p2