bpo-39761: dtrace build fix for Linux and non Linux systems.

[devnexen]

https://bugs.python.org/issue39761

[codecov]

Codecov Report

Merging #18672 into master will increase coverage by 2.71%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master   #18672       +/-   ##
===========================================
+ Coverage   79.41%   82.13%    +2.71%     
===========================================
  Files         385     1955     +1570     
  Lines      174631   584458   +409827     
  Branches        0    44477    +44477     
===========================================
+ Hits       138683   480019   +341336     
- Misses      35948    94795    +58847     
- Partials        0     9644     +9644     

Impacted Files	Coverage Δ
Modules/_decimal/libmpdec/umodarith.h	80.76% <0.00%> (-19.24%)	⬇️
Modules/clinic/spwdmodule.c.h	58.33% <0.00%> (-3.21%)	⬇️
Modules/clinic/resource.c.h	78.57% <0.00%> (-2.68%)	⬇️
Modules/clinic/_pickle.c.h	62.40% <0.00%> (-2.33%)	⬇️
Modules/clinic/signalmodule.c.h	71.51% <0.00%> (-2.32%)	⬇️
Python/clinic/marshal.c.h	77.77% <0.00%> (-2.23%)	⬇️
Modules/clinic/_weakref.c.h	77.77% <0.00%> (-2.23%)	⬇️
Modules/clinic/_queuemodule.c.h	78.08% <0.00%> (-2.17%)	⬇️
Modules/_multiprocessing/clinic/posixshmem.c.h	66.66% <0.00%> (-2.09%)	⬇️
Objects/clinic/moduleobject.c.h	78.94% <0.00%> (-2.01%)	⬇️
... and 1838 more

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[hroncok]

I can verify this fixes the build on Fedora. Not sure if this is the best or even the proper fix, not sure how it affects other unix-ish systems, but it get's the job done for us.

[encukou]

I don't think Linux should be an exception. ISTM that the issue is not with Linux, but rather with empty DFLAGS.

[encukou]

See #18766 for another approach.

[ned-deily]

It appears this issue was resolved with the change in #18766. Thanks for submitting the PR and sorry this remained open for so long.