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.

ConflictSet.cpp

@@ -3080,7 +3080,7 @@ Node *firstGeqPhysical(Node *n, const TrivialSpan key) {
 #define PRESERVE_NONE
 #endif
 
-#if __has_attribute(musttail) && __has_attribute(preserve_none)
+#if __has_attribute(musttail)
 constexpr bool kEnableInterleaved = true;
 #else
 constexpr bool kEnableInterleaved = false;
@@ -5040,20 +5040,22 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     assert(allPointWrites || sorted);
 #endif
 
-    if (kEnableInterleaved && count > 1) {
-      interleavedWrites(writes, count, InternalVersionT(writeVersion));
-    } else {
-      for (int i = 0; i < count; ++i) {
-        const auto &w = writes[i];
-        auto begin = TrivialSpan(w.begin.p, w.begin.len);
-        auto end = TrivialSpan(w.end.p, w.end.len);
-        if (w.end.len > 0) {
-          addWriteRange(rootParent->children[0], begin, end,
-                        InternalVersionT(writeVersion), &writeContext);
-        } else {
-          addPointWrite(rootParent->children[0], begin,
-                        InternalVersionT(writeVersion), &writeContext);
-        }
+    if constexpr (kEnableInterleaved) {
+      if (count > 1) {
+        interleavedWrites(writes, count, InternalVersionT(writeVersion));
+        return;
+      }
+    }
+    for (int i = 0; i < count; ++i) {
+      const auto &w = writes[i];
+      auto begin = TrivialSpan(w.begin.p, w.begin.len);
+      auto end = TrivialSpan(w.end.p, w.end.len);
+      if (w.end.len > 0) {
+        addWriteRange(rootParent->children[0], begin, end,
+                      InternalVersionT(writeVersion), &writeContext);
+      } else {
+        addPointWrite(rootParent->children[0], begin,
+                      InternalVersionT(writeVersion), &writeContext);
       }
     }
   }