Reverse order of CMAKE_CXX_FLAGS initialization

The old order caused cmake in Mac OSX to not detect c++11. This fixes the problem.

CMakeLists.txt

@@ -45,12 +45,6 @@ message(STATUS "Configured to compile in ${CMAKE_BUILD_TYPE} mode.")
 SET(CMAKE_CXX_FLAGS_DEBUG "-g -Wall -D_REENTRANT")
 SET(CMAKE_CXX_FLAGS_RELEASE "-O3 -D_REENTRANT")
 
-if(UNIX)
-  # GCC is not strict enough by default, so enable most of the warnings.
-  set(CMAKE_CXX_FLAGS
-    "${CMAKE_CXX_FLAGS} -Werror=all -Werror=extra -Wno-unknown-pragmas -Wno-sign-compare -Wno-unused-parameter -Wno-missing-field-initializers")
-endif(UNIX)
-
 #Set compiler according C++11 support
 include(CheckCXXCompilerFlag)
 CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
@@ -65,6 +59,12 @@ else()
         message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
 endif()
 
+if(UNIX)
+  # GCC is not strict enough by default, so enable most of the warnings.
+  set(CMAKE_CXX_FLAGS
+    "${CMAKE_CXX_FLAGS} -Werror=all -Werror=extra -Wno-unknown-pragmas -Wno-sign-compare -Wno-unused-parameter -Wno-missing-field-initializers")
+endif(UNIX)
+
 
 #OPTION(BUILD_DOC "Build Documentation" OFF)
 OPTION(BUILD_TESTS "Build Unit tests" ON)