Just manually verified that PR19377, when compiled against xlc - crashes during make:

	rm -f libpython3.9d.a
	ar rcs libpython3.9d.a Modules/getbuildinfo.o  Parser/acceler.o  Parser/grammar1.o  Parser/listnode.o  Parser/node.o  Parser/parser.o  Parser/token.o   Parser/myreadline.o Parser/parsetok.o Parser/tokenizer.o  Objects/abstract.o  Objects/accu.o  Objects/boolobject.o  Objects/bytes_methods.o  Objects/bytearrayobject.o  Objects/bytesobject.o  Objects/call.o  Objects/capsule.o  Objects/cellobject.o  Objects/classobject.o  Objects/codeobject.o  Objects/complexobject.o  Objects/descrobject.o  Objects/enumobject.o  Objects/exceptions.o  Objects/genobject.o  Objects/fileobject.o  Objects/floatobject.o  Objects/frameobject.o  Objects/funcobject.o  Objects/interpreteridobject.o  Objects/iterobject.o  Objects/listobject.o  Objects/longobject.o  Objects/dictobject.o  Objects/odictobject.o  Objects/memoryobject.o  Objects/methodobject.o  Objects/moduleobject.o  Objects/namespaceobject.o  Objects/object.o  Objects/obmalloc.o  Objects/picklebufobject.o  Objects/rangeobject.o  Objects/setobject.o  Objects/sliceobject.o  Objects/structseq.o  Objects/tupleobject.o  Objects/typeobject.o  Objects/unicodeobject.o  Objects/unicodectype.o  Objects/weakrefobject.o  Python/_warnings.o  Python/Python-ast.o  Python/asdl.o  Python/ast.o  Python/ast_opt.o  Python/ast_unparse.o  Python/bltinmodule.o  Python/ceval.o  Python/codecs.o  Python/compile.o  Python/context.o  Python/dynamic_annotations.o  Python/errors.o  Python/frozenmain.o  Python/future.o  Python/getargs.o  Python/getcompiler.o  Python/getcopyright.o  Python/getplatform.o  Python/getversion.o  Python/graminit.o  Python/hamt.o  Python/import.o  Python/importdl.o  Python/initconfig.o  Python/marshal.o  Python/modsupport.o  Python/mysnprintf.o  Python/mystrtoul.o  Python/pathconfig.o  Python/peephole.o  Python/preconfig.o  Python/pyarena.o  Python/pyctype.o  Python/pyfpe.o  Python/pyhash.o  Python/pylifecycle.o  Python/pymath.o  Python/pystate.o  Python/pythonrun.o  Python/pytime.o  Python/bootstrap_hash.o  Python/structmember.o  Python/symtable.o  Python/sysmodule.o  Python/thread.o  Python/traceback.o  Python/getopt.o  Python/pystrcmp.o  Python/pystrtod.o  Python/pystrhex.o  Python/dtoa.o  Python/formatter_unicode.o  Python/fileutils.o  Python/dynload_shlib.o        Modules/config.o  Modules/getpath.o  Modules/main.o  Modules/gcmodule.o  Modules/posixmodule.o  Modules/errnomodule.o  Modules/pwdmodule.o  Modules/_sre.o  Modules/_codecsmodule.o  Modules/_weakref.o  Modules/_functoolsmodule.o  Modules/_operator.o  Modules/_collectionsmodule.o  Modules/_abc.o  Modules/itertoolsmodule.o  Modules/atexitmodule.o  Modules/signalmodule.o  Modules/_stat.o  Modules/timemodule.o  Modules/_threadmodule.o  Modules/_localemodule.o  Modules/_iomodule.o Modules/iobase.o Modules/fileio.o Modules/bytesio.o Modules/bufferedio.o Modules/textio.o Modules/stringio.o  Modules/faulthandler.o  Modules/_tracemalloc.o Modules/hashtable.o  Modules/symtablemodule.o  Modules/xxsubtype.o  Python/frozen.o
	./Modules/makexp_aix Modules/python.exp . libpython3.9d.a;  xlc_r     -Wl,-bE:Modules/python.exp -lld -o python Programs/python.o libpython3.9d.a -lintl -ldl  -lm   -lm 
	 ./python -E -S -m sysconfig --generate-posix-vars ; if test $? -ne 0 ; then  echo "generate-posix-vars failed" ;  rm -f ./pybuilddir.txt ;  exit 1 ;  fi
Objects/genobject.c:127: _PyObject_GC_TRACK: Assertion "!(((PyGC_Head *)(op)-1)->_gc_next != 0)" failed: object already tracked by the garbage collector
Enable tracemalloc to get the memory block allocation traceback
object address  : 30084150
object refcount : 0
object type     : 20013aa8
object type name: generator
object repr     : <refcnt 0 at 30084150>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: core initialized
Current thread 0x00000001 (most recent call first):
  File "<frozen importlib._bootstrap_external>", line 1593 in _setup
  File "<frozen importlib._bootstrap_external>", line 1634 in _install
  File "<frozen importlib._bootstrap>", line 1189 in _install_external_importers
/bin/sh: 24117648 IOT/Abort trap(coredump)
make: 1254-004 The error code from the last command is 134.
Stop.

FYI: about two hours ago I verified that xlc and 08050e959e6c40839cd2c9e5f6a4fd1513e3d605 : bpo-40147: Fix a compiler warning on Windows in Python/compile.c (GH-19389)

all was green.