Odd FMM failures with Pocl 0.14

See for example https://gitlab.tiker.net/inducer/pytential/-/jobs/27447

This test:

pycl test_layer_pot.py 'test_off_surface_eval_vs_direct(cl._csc)' 

succeeds on cold cache with both pocl 0.13 and 0.14. With pocl 0.14, a warm-cache run yields an error above the tolerance. Pocl 0.13 continues to succeed.

• Deleting the pocl cache between runs makes no difference.
• Deleting the loopy caches between runs makes no difference.

The error:

on top of this potential:

makes it look like this is an interaction list issue.

@mattwala, any ideas?