s390x Fedora Clang 3.x buildbot:
https://buildbot.python.org/all/#/builders/3/builds/1385

This change may be caused by this buildbot configuration change:
https://github.com/python/buildmaster-config/commit/8fbb7492d4509df074750bc1a8ea69812ff53aae

---
0:05:48 load avg: 7.72 [215/432/1] test_lib2to3 crashed (Exit code -11) -- running: (...)
Fatal Python error: Segmentation fault

Current thread 0x000003ff94176710 (most recent call first):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 845 in generate_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 785 in _recursive_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  (...)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  ...

Extension modules: _testcapi (total: 1)
---

and

---
0:06:29 load avg: 7.50 [245/432/2] test_json crashed (Exit code -11) -- running: (...)
Fatal Python error: Segmentation fault

Current thread 0x000003ffbccf6710 (most recent call first):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 439 in _iterencode
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 325 in _iterencode_list
  (...)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 439 in _iterencode
  ...

Extension modules: _testcapi (total: 1)
---

test.pythoninfo difference between successful build 1383 and failing build 1385:

* Py_DEBUG: No => Yes
* pymem.allocator: pymalloc => pymalloc_debug
* sysconfig[CFLAGS]: -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall
  => sysconfig[CFLAGS]: -Wsign-compare -g -O0 -Wall