Fix OS X build

Change-Id: If0465b73843ad1a489fa66318a689801def3f0f0
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f50c491..be7bddd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -51,16 +51,14 @@
 # source_group(Compiler FILES ${FlatBuffers_Compiler_SRCS})
 # source_group(Tests FILES ${FlatBuffers_Tests_SRCS})
 
-if(CMAKE_COMPILER_IS_GNUCXX)
-  add_definitions("-std=c++0x")
-  add_definitions("-Wall")
-endif()
-if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
-  add_definitions("-std=c++0x")
+if(APPLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -stdlib=libc++ -Wall")
+elseif(CMAKE_COMPILER_IS_GNUCXX OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -Wall")
 endif()
 
 if(FLATBUFFERS_CODE_COVERAGE)
-  add_definitions("-g -fprofile-arcs -ftest-coverage")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -fprofile-arcs -ftest-coverage")
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fprofile-arcs -ftest-coverage")
 endif()