Prefer libc++ on Apple if available

CMakeLists.txt

@@ -241,6 +241,7 @@ endif()
 include(CheckCXXCompilerFlag)
 check_cxx_compiler_flag( "-std=c++11" CXX11_FOUND )
 check_cxx_compiler_flag( "-std=c++0x" CXX0X_FOUND )
+check_cxx_compiler_flag( "-stdlib=libc++" LIBCPP_FOUND )
 if(CXX11_FOUND)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 elseif(CXX0X_FOUND)
@@ -249,6 +250,9 @@ else()
     message(STATUS "${CMAKE_CXX_COMPILER} does not support C++11, please use a
     different compiler")
 endif()
+if(LIBCPP_FOUND AND APPLE)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
+endif()
 
 macro_optional_find_package(Echonest 2.2.0)
 macro_log_feature(ECHONEST_FOUND "Echonest" "Qt library for communicating with The Echo Nest" "http://projects.kde.org/libechonest" TRUE "" "libechonest 2.2.0 is needed for dynamic playlists and the infosystem")