MSVC's Debug code generator does not dead-code-eliminate after an `if constexpr`
chain whose branches all return, so the fallthrough `return` after the chain is
flagged C4702 (unreachable) on instantiations where one of the branches is
selected. Release builds optimize the dead path out and never complain.
Restructure two places so the fallback lives inside an explicit `else` /
returning helper instead of a fallthrough:
* `enforce_bounds()` (quantity_point.h): wrap the `return q;` fallback in
`else { return q; }` after the existing `if constexpr` chain.
* `compare_quantities()` (quantity.h): hoist the floating-point / already-widest
fallback into a local `fallback_cmp` lambda invoked from both arms of the
`if constexpr` chain. Keeps the existing float-equal suppression.
For `CHECK_THROWS_AS` in constrained_test.cpp, Catch2's macro expands into a
try/catch whose catch arm becomes unreachable when the body calls a `[[noreturn]]`
function; suppress C4702 around that one TEST_CASE since the macro is not ours
to restructure.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Mateusz Pusz