188.8.131.52: fix test failures on PPC and elsewhere
* Most of the failures were test that cannot pass due to missing
bits of DX implementation -- stack allocatable vectors and
* Mark backtrace test 353 as expected to fail on PPC as well.
* Don't declare *HANDLER-CLUSTERS* as dynamic-extent on platforms
that do not support DX fixed-alloc, since it will just give
a spurious compiler note.