Fix release and coverage CI failures

* ConflictSet.cpp: enable the interleaved read/write path whenever
  musttail is available, falling back to the default calling convention
  when preserve_none is not supported. This prevents a large block of
  compiled-but-dead code from being counted in coverage.

* CMakeLists.txt: detect which arch-specific hardening-check options the
  installed hardening-check binary supports, including the newer
  hyphenated spellings, so the release test no longer fails with an
  unknown option.

* .gitea/workflows/ci.yml: build the coverage job with
  -DUSE_SIMD_FALLBACK=ON so AVX512-only functions that cannot execute on
  the CI runners are not counted against line coverage.

.gitea/workflows/ci.yml

@@ -256,7 +256,8 @@ jobs:
           rm -rf build
           cmake -S . -B build -G Ninja -DCMAKE_CXX_COMPILER_LAUNCHER=ccache \
             -DCMAKE_C_FLAGS=--coverage -DCMAKE_CXX_FLAGS=--coverage \
-            -DCMAKE_BUILD_TYPE=Debug -DDISABLE_TSAN=ON
+            -DCMAKE_BUILD_TYPE=Debug -DDISABLE_TSAN=ON \
+            -DUSE_SIMD_FALLBACK=ON
           ninja -C build
           ccache -s