[gdb/testsuite] Fix KPASS in gdb.ada/arrayptr.exp

[gdb/testsuite] Fix KPASS in gdb.ada/arrayptr.exp

On openSUSE Leap 15.3 I run into:
...
KPASS: gdb.ada/arrayptr.exp: scenario=minimal: print pa_ptr.all \
  (PRMS minimal encodings)
KPASS: gdb.ada/arrayptr.exp: scenario=minimal: print pa_ptr(3) \
  (PRMS minimal encodings)
KPASS: gdb.ada/arrayptr.exp: scenario=minimal: print pa_ptr.all(3) \
  (PRMS minimal encodings)
...

The test-case KFAILs some tests.  However, the analysis in the corresponding
PR talks of a compiler problem, so it should use XFAILs instead.

The KFAILs are setup for pre-gcc-12, but apparantly the fix has been
backported to system compiler 7.5.0, hence the KPASS.

Fix this by:
- using an XFAIL instead of a KFAIL
- matching the specific gdb output that corresponds to the XFAILs
  (reproduced on Fedora 34).

Tested on x86_64-linux, specifically openSUSE Leap 15.3 and Fedora 34.