Cmake improvement

[JohanMabille]

Addresses the comments from apache/iceberg-cpp#44 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.24%. Comparing base (532bf48) to head (79aec32).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #348      +/-   ##
==========================================
- Coverage   90.34%   90.24%   -0.11%     
==========================================
  Files          84       84              
  Lines        6516     6531      +15     
==========================================
+ Hits         5887     5894       +7     
- Misses        629      637       +8     

Flag	Coverage Δ
unittests	90.24% <ø> (-0.11%)	⬇️

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