Quoting from the bug report:

The pstack library has been included in MySQL since version
4.0.0. It's useless and should be removed.

Details: According to its own documentation, pstack only works
on Linux on x86 in 32 bit mode and requires LinuxThreads and a
statically linked binary. It doesn't really support any Linux
from 2003 or later and doesn't work on any other OS.

The --enable-pstack option is thus deprecated and has no effect.