Using Msan

# Build llvm

cmake -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ \
  -DLLVM_USE_SANITIZER="MemoryWithOrigins"
  -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR \
  -DCMAKE_BUILD_TYPE=RelWithDebInfo -G Ninja \
  -S runtimes -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
  path/to/llvm

ninja -j32 install-cxx install-cxxabi

# Sanitize project

# May also need to set CMAKE_C_FLAGS
set(CMAKE_CXX_FLAGS "-g -fsanitize=memory -fno-omit-frame-pointer -fsanitize-memory-track-origins -nostdinc++ -isystem ${INSTALL_DIR}/include/c++/v1")

# May also need to set and CMAKE_SHARED_LINKER_FLAGS
set(CMAKE_EXE_LINKER_FLAGS "-Wno-error=unused-command-line-argument -fsanitize=memory -stdlib=libc++ -lc++abi -Wl,-rpath ${INSTALL_DIR}/lib -L${INSTALL_DIR}/lib")

In case of errors check https://stackoverflow.com/questions/56454026/building-libc-with-memorysanitizer-instrumentation-fails-due-to-memorysanitize