Fix cxx test

Fix two CMake bugs:

CMake: Remove test DEAL_II_HAVE_CXX11_ICCBOOSTSIGNALSBUG_OK

 * We cannot sanely test for the icc-boost-signals2 regression prior to boost setup. And after
  boost setup it is incredibly ugly to do so because DEAL_II_WITH_STDCXX11 is
  already processed. Therefore, just remove the configure time check.

CMake: Bugfix: Also sanitize (cpp) macros in enable_if_links