Compilation failure due to missing symbol pthread_atfork

#10614 introduced usage of pthread_atfork if the pthread header was found. However this requires adding -lpthread or -pthread to the compiler flags so the symbols can be found.

This kinda works on x86 platforms because Python is usually build with pthreads already and the dynamic library contains all the symbols. However on e.g. Power9 libpthread is a linker script contained a static part which contains e.g. pthread_atfork which does now not get linked and hence usage fails with

File "/tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/__init__.py", line 156, in <module>
  from . import fft
File "/tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/fft/__init__.py", line 81, in <module>
  from ._helper import next_fast_len
File "/tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/fft/_helper.py", line 4, in <module>
  from . import _pocketfft
File "/tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/fft/_pocketfft/__init__.py", line 3, in <module>
  from .basic import *
File "/tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/fft/_pocketfft/basic.py", line 8, in <module>
  from . import pypocketfft as pfft
ImportError: /tmp/easybuild-tmp/eb-QqGzOJ/tmp81X11X/lib/python3.7/site-packages/scipy/fft/_pocketfft/pypocketfft.cpython-37m-powerpc64le-linux-gnu.so: undefined symbol: pthread_atfork
(at easybuild/tools/run.py:529 in parse_cmd_output)

Proposed solution: Add -pthread or -lpthread to the link flags.

[peterbell10]

That’s find @Flamefire. I think we’ve adequately diagnosed the problem without the log.

[Flamefire]

@peterbell10 As the logs are gone and recreating them takes a couple hours: Do you still need the logs? IMO my analysis above is complete and #11324 fixes the problem so I don’t know of what help the logs would be.