Testsuite: recomp011 and recomp015 are fixed on powerpc

These tests have been fixed but not tested and re-enabled on big-endian powerpc (see comments in #11260 (closed) and #11323 (closed)).

For the record, the testsuite result on a PowerPC64 big-endian:

Unexpected results from:
TEST="AtomicFetch CallerCc1 CallerCc2 CallerCc3 GHCiPrimCall LargeBCO T10620 T10667 T11649 T13658 T14779a T14779b T14868 T14894 T15155l T17586 T20112 T21152 T22187 T5681 T7275 T7571 T8131b callstack001 debug num009 process011 recomp011 recomp015 staticcallstack001 staticcallstack002 topHandler01 toplevel_scc_1 tso_and_stack_closures"

SUMMARY for test run started at Mon Oct 16 18:49:06 2023
2:49:18.310314 spent to go through
    9776 total tests, which gave rise to
   54084 test cases, of which
   44216 were skipped
       7 had missing libraries

    9674 expected passes
     123 expected failures

       0 caused framework failures
       0 caused framework warnings
       2 unexpected passes
      37 unexpected failures
       0 unexpected stat failures
      32 fragile tests

Unexpected passes:
   /tmp/ghctest-jnoekjs8/test   spaces/testsuite/tests/driver/recomp011/recomp011.run  recomp011 [unexpected] (normal)
   /tmp/ghctest-jnoekjs8/test   spaces/testsuite/tests/driver/recomp015/recomp015.run  recomp015 [unexpected] (normal)