I highly recommend this article written by my colleagues Serge Guelton and Yannis Juglaret about a truly hard-to-parse issue that affected #Firefox users on old Ubuntu installations.
It's a cautionary tale about how complex builds can be affected by subtle compiler/linker flags. Also, C++ is hard and making modern C++ work on older platforms is painful and full of pitfalls.
https://hacks.mozilla.org/2024/01/option-soup-the-subtle-pitfalls-of-combining-compiler-flags/
@gabrielesvelto OpenMW had a recent issue along these lines, where variable types not being entirely supported uniformly across platforms resulted in (on Linux) animations stopping working correctly.