message: Add CLANG_USE_BUNDLED_LIBC++ to cmake
diff: @@ -11,6 +11,7 @@ set(CLANG_DOWNLOAD_LOCATION ${CMAKE_BINARY_DIR}
  option(SYSTEM_CLANG "Use system installation of Clang instead of \
  downloading Clang" OFF)
  option(ASAN "Compile with address sanitizers" OFF)
  +option(CLANG_USE_BUNDLED_LIBC++ "Let Clang use bundled libc++" OFF)
  # Sources for the executable are specified at end of CMakeLists.txt
  add_executable(ccls "")
  @@ -81,6 +82,16 @@ if(NOT SYSTEM_CLANG)
  download_and_extract_clang(${CLANG_VERSION} ${CLANG_DOWNLOAD_LOCATION})
  # Used by FindClang
  set(CLANG_ROOT ${DOWNLOADED_CLANG_DIR})
  +
  + if(${CMAKE_CXX_COMPILER_ID} STREQUAL Clang AND CLANG_USE_BUNDLED_LIBC++)
  + message(STATUS "Using bundled libc++")
  + target_compile_options(ccls PRIVATE -stdlib=libc++)
  + target_include_directories(ccls PRIVATE ${CLANG_ROOT}/include/c++/v1)
  + target_link_libraries(ccls PRIVATE ${CLANG_ROOT}/lib/libc++.a
  + ${CLANG_ROOT}/lib/libc++abi.a
  + ${CLANG_ROOT}/lib/libc++experimental.a)
  + endif()
  +
  else()
  message(STATUS "Using system Clang")
  endif()
  