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

@@ -19,9 +19,15 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            clang git nodejs pre-commit
+            clang-21 git nodejs pre-commit
+          for tool in clang clang++; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -57,12 +63,18 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            build-essential ccache clang cmake gcc g++ \
+            build-essential ccache clang-21 cmake gcc g++ \
-            libc6-dbg llvm mold ninja-build python3 valgrind zstd
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -124,14 +136,20 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            biber build-essential ccache clang cmake devscripts \
+            biber build-essential ccache clang-21 cmake devscripts \
-            latexmk libc6-dbg llvm mold ninja-build rpm \
+            latexmk libc6-dbg llvm-21 lld-21 mold ninja-build rpm \
             texlive-bibtex-extra texlive-fonts-recommended \
             texlive-latex-extra texlive-pictures valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-$(dpkg --print-architecture)/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:
@@ -212,12 +230,18 @@ jobs:
 
       - name: Install dependencies
         run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
           sudo apt-get update -qq
           sudo apt-get install -y \
-            build-essential ccache clang cmake gcovr \
+            build-essential ccache clang-21 cmake gcovr \
-            libc6-dbg llvm mold ninja-build python3 valgrind zstd
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
           sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
             -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
 
       - uses: actions/cache@v4
         with:

CMakeLists.txt

@@ -391,21 +391,18 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
         COMMAND ${HARDENING_CHECK} --help
         OUTPUT_VARIABLE hardening_check_help
         ERROR_VARIABLE hardening_check_help
-        OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE
+        OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE)
-        RESULT_VARIABLE hardening_check_help_result)
       set(hardening_check_arch_flags "")
-      if(hardening_check_help_result EQUAL 0)
+      # Control flow integrity (CET) is x86-only and branch protection (PAC/BTI)
-        # Control flow integrity (CET) is x86-only and branch protection
+      # is arm64-only, so ignore whichever doesn't apply.
-        # (PAC/BTI) is arm64-only, so ignore whichever doesn't apply.
+      if(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64 OR CMAKE_SYSTEM_PROCESSOR
-        if(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64 OR CMAKE_SYSTEM_PROCESSOR
+                                                    STREQUAL arm64)
-                                                      STREQUAL arm64)
+        if(hardening_check_help MATCHES "nocfprotection")
-          if(hardening_check_help MATCHES "nocfprotection")
+          list(APPEND hardening_check_arch_flags --nocfprotection)
-            list(APPEND hardening_check_arch_flags --nocfprotection)
+        endif()
-          endif()
+      else()
-        else()
+        if(hardening_check_help MATCHES "nobranchprotection")
-          if(hardening_check_help MATCHES "nobranchprotection")
+          list(APPEND hardening_check_arch_flags --nobranchprotection)
-            list(APPEND hardening_check_arch_flags --nobranchprotection)
-          endif()
         endif()
       endif()
       add_test(