replace complexity with simplicity for faster libc++ setup

.github/libcxx-setup.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+# Checkout LLVM sources
+#git clone --depth=1 https://github.com/llvm/llvm-project.git llvm-project
+#
+## Setup libc++ options
+#if [ -z "$BUILD_32_BITS" ]; then
+#  export BUILD_32_BITS=OFF && echo disabling 32 bit build
+#fi
+#
+## Build and install libc++ (Use unstable ABI for better sanitizer coverage)
+#cd ./llvm-project
+#cmake -DCMAKE_C_COMPILER=${CC}                  \
+#      -DCMAKE_CXX_COMPILER=${CXX}               \
+#      -DCMAKE_BUILD_TYPE=RelWithDebInfo         \
+#      -DCMAKE_INSTALL_PREFIX=/usr               \
+#      -DLIBCXX_ABI_UNSTABLE=OFF                 \
+#      -DLLVM_USE_SANITIZER=${LIBCXX_SANITIZER}  \
+#      -DLLVM_BUILD_32_BITS=${BUILD_32_BITS}     \
+#      -DLLVM_ENABLE_RUNTIMES='libcxx;libcxxabi' \
+#      -S llvm -B llvm-build -G "Unix Makefiles"
+#make -C llvm-build -j3 cxx cxxabi
+#sudo make -C llvm-build install-cxx install-cxxabi
+#cd ..
+
+sudo apt update
+sudo apt -y install libc++-dev libc++abi-dev

.github/workflows/sanitizer.yml

@@ -45,6 +45,12 @@ jobs:
         echo "EXTRA_FLAGS=-g -O2 -fno-omit-frame-pointer -fsanitize=thread -fno-sanitize-recover=all" >> $GITHUB_ENV
         echo "LIBCXX_SANITIZER=Thread" >> $GITHUB_ENV
 
+    - name: fine-tune asan options
+      # in clang+asan we get an error from std::regex. ignore it.
+      if: matrix.sanitizer == 'asan' && matrix.compiler == 'clang'
+      run: |
+        echo "ASAN_OPTIONS=alloc_dealloc_mismatch=0" >> $GITHUB_ENV
+
     - name: setup clang
       if: matrix.compiler == 'clang'
       uses: egor-tensin/setup-clang@v1
@@ -68,7 +74,7 @@ jobs:
     - name: install llvm stuff
       if: matrix.compiler == 'clang'
       run: |
-        "${GITHUB_WORKSPACE}/.github/.libcxx-setup.sh"
+        "${GITHUB_WORKSPACE}/.github/libcxx-setup.sh"
         echo "EXTRA_CXX_FLAGS=\"-stdlib=libc++\"" >> $GITHUB_ENV
 
     - name: create build environment