This is a series of small bugfixes for clang and icc configuration:

* Add a configure time check for a bug in icc

   icc-14*, icc-15* does not play nicely with enabled -std=c++11 and
   boost::signals2, disable C++11 support in this case.

   [1] https://software.intel.com/en-us/forums/topic/515966

 * CMake: Bugfix: Correctly detect unsupported flags in case of clang

   The clang compiler frontend is very conservative in not issuing an error
   for unsupported compile flags but that are valid for gcc. Therefore, also
   supply "-Werror" for the clang compiler in all 'ENABLE_IF_SUPPORTED' tests.

 * CMake: Bugfix: Replace all "-" by "_" for some internal variable name

   ENABLE_IF_SUPPORTED incorrectly exported invalid (cpp) macro definitions
   containing a dash "-". Fix this by replacing all dashes with underscores
   "_".