message: Add LLVM_ENABLE_RTTI (default: OFF) to allow linking against Arch Linux extra/{llvm,clang} (-DLLVM_ENABLE_RTTI=ON)
diff: @@ -10,6 +10,7 @@ set(CLANG_DOWNLOAD_LOCATION ${CMAKE_BINARY_DIR}
  option(SYSTEM_CLANG "Use system installation of Clang instead of \
  downloading Clang" OFF)
  option(ASAN "Compile with address sanitizers" OFF)
  +option(LLVM_ENABLE_RTTI "-fno-rtti if OFF. This should match LLVM libraries" OFF)
  option(CLANG_USE_BUNDLED_LIBC++ "Let Clang use bundled libc++" OFF)
  option(USE_SHARED_LLVM "Link against libLLVM.so instead separate LLVM{Option,Support,...}" OFF)
  @@ -34,8 +35,12 @@ if(NOT CYGWIN)
  set_property(TARGET ccls PROPERTY CXX_EXTENSIONS OFF)
  endif()
  -# To link against LLVM libraries (usually compiled with -fno-rtti)
  +if(NOT LLVM_ENABLE_RTTI)
  + # releases.llvm.org libraries are compiled with -fno-rtti
  + # The mismatch between lib{clang,LLVM}* and ccls can make libstdc++ std::make_shared return nullptr
  + # _Sp_counted_ptr_inplace::_M_get_deleter
  target_compile_options(ccls PRIVATE -fno-rtti)
  +endif()
  # CMake sets MSVC for both MSVC and Clang(Windows)
  if(MSVC)
  