Fix quadmath detection in CMake for Cross-Compilation

[mborland]

@anarthal Can you please see if this change breaks your alpine environment? I added the CheckCXXSourceRuns to fix that environment but now apparently this breaks cross compilation: #193 (comment)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.84%. Comparing base (0c8358a) to head (b024cfc).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #284      +/-   ##
===========================================
- Coverage    94.92%   94.84%   -0.08%     
===========================================
  Files           73       73              
  Lines         9186     8986     -200     
===========================================
- Hits          8720     8523     -197     
+ Misses         466      463       -3     

see 47 files with indirect coverage changes

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[anarthal]

Seems to be fine: https://github.com/anarthal/servertech-chat/actions/runs/18907969430/job/53970789363

[mborland]

Seems to be fine: https://github.com/anarthal/servertech-chat/actions/runs/18907969430/job/53970789363

Cool. Thanks for checking.