[Bug c++/120955] [15/16 Regression] 50 % increase in data segment size on avr-gcc for -Os

[fiesh at zefix dot tv via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120955

--- Comment #20 from fiesh at zefix dot tv ---
Actually, this is not a good reduction since the original unreduced test case
does not rely on `-fimplicit-constexpr`.  (One needs to modify the source
trivially by removing the call to the non-constexpr std::abs.)

So I'll try to reduce again, without accidentally relying on
`-fimplicit-constexpr`.