fix cpu affinity check

[remicollet]

Without _GNU_SOURCE,

configure:13553: checking for cpu affinity
configure:13577: cc -c  -O2 -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64   -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer   conftest.c >&5
conftest.c: In function 'main':
conftest.c:50:9: error: implicit declaration of function 'CPU_ZERO' [-Wimplicit-function-declaration]
   50 |         CPU_ZERO(&cpu_set);
      |         ^~~~~~~~
configure:13577: $? = 1

Fix happen with recent GCC version 14.2 when implicit-function-declaration is now an error.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.91%. Comparing base (3e1a1f8) to head (5630753).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5624      +/-   ##
==========================================
- Coverage   70.91%   70.91%   -0.01%     
==========================================
  Files         109      109              
  Lines       16805    16805              
  Branches     3073     3073              
==========================================
- Hits        11918    11917       -1     
- Misses       4831     4832       +1     
  Partials       56       56              

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