It appears that the submitted patch causes a

-DSYSTEM_MALLOC

build of Tcl to have the same effect that a build leaving out

-DUSE_THREAD_ALLOC=1

already achieves.

We don't need two knobs to do the same thing.

It would be useful, of course, to have a repeatable
demo of the crash for analysis and fix.

Since this bug was submitted, some code changes have
gone into tclThreadAlloc.c .  Hard to know whether
they had an impact on this matter.