Add task-taskwait-nested test to LIT_XFAIL on ppc

This test fails on ppc, so add it to the XFAIL list like the other
similar tests. It would be better to fix the root cause, but in the
meantime, add it to XFAIL to unblock the snapshot builds.

Author: tbaederr

llvm.spec

@@ -2330,7 +2330,6 @@ test_list_filter_out+=("libomp :: worksharing/for/omp_collapse_one_int.c")
 test_list_filter_out+=("libomp :: parallel/bug63197.c")
 test_list_filter_out+=("libomp :: tasking/issue-69733.c")
 test_list_filter_out+=("libarcher :: races/task-taskgroup-unrelated.c")
-test_list_filter_out+=("libarcher :: races/task-taskwait-nested.c")
 
 # The following tests have been failing intermittently.
 # Issue upstream: https://github.com/llvm/llvm-project/issues/127796
@@ -2394,6 +2393,7 @@ export LIT_XFAIL="$LIT_XFAIL;races/task-dependency.c"
 export LIT_XFAIL="$LIT_XFAIL;races/task-taskgroup-unrelated.c"
 export LIT_XFAIL="$LIT_XFAIL;races/task-two.c"
 export LIT_XFAIL="$LIT_XFAIL;races/taskwait-depend.c"
+export LIT_XFAIL="$LIT_XFAIL;races/task-taskwait-nested.c"
 export LIT_XFAIL="$LIT_XFAIL;reduction/parallel-reduction-nowait.c"
 export LIT_XFAIL="$LIT_XFAIL;reduction/parallel-reduction.c"
 export LIT_XFAIL="$LIT_XFAIL;task/omp_task_depend_all.c"