Fix macOS SSE support not detected correctly after recent changes

Due to moving the code the test binary was incorrectly compiled with OpenMP
flags. Move setting of the OpenMP flags to the appropriate place.

CMakeLists.txt

@@ -1215,6 +1215,7 @@ if(WITH_OPENMP)
     if(NOT WITH_OPENMP_STATIC)
       string(APPEND CMAKE_C_FLAGS " ${OpenMP_C_FLAGS}")
       string(APPEND CMAKE_CXX_FLAGS " ${OpenMP_CXX_FLAGS}")
+      string(APPEND CMAKE_EXE_LINKER_FLAGS " ${OpenMP_LINKER_FLAGS}")
     else()
       # Typically avoid adding flags as defines but we can't
       # pass OpenMP flags to the linker for static builds, meaning