fix: constexpr function local must not be static (GCC 11/12 portability) - #390
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`value()` declared its `needs_fp` compile-time selector as a `static constexpr` local. A `static` local in a `constexpr` function is only well-formed from GCC 13 / Clang 17 (P2647); GCC 11 and 12 reject it with "declared 'static' in 'constexpr' function", so a translation unit that instantiates `value()` fails to compile there. The variable is used only as a `std::conditional_t` condition — its address is never taken and it is never materialized — so dropping `static` is behavior-identical on every compiler while restoring the build on GCC 11/12.
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unit::value()declared itsneeds_fpcompile-time selector as astatic constexprlocal. Astaticlocal inside aconstexprfunction is only well-formed from GCC 13 / Clang 17 (P2647); GCC 11 and 12 reject it:so a translation unit that instantiates
value()fails to compile on those compilers. (Surfaced by a downstream project whose CI builds on GCC 11.)needs_fpis used only as astd::conditional_tcondition — its address is never taken and it is never materialized — so droppingstaticis behavior-identical on every compiler while restoring the build on GCC 11/12.Verified: full suite 467/467 on GCC 15; and under a GCC 11 container the pre-fix tree fails with the error above while the fixed tree compiles. The declared support floor stays GCC 13 (this is a free portability widening, not a new supported target).