add exceptions case in the configure script. This is mainly used by

Fermilab experiments using KCC compilers. Use:
  ./configure linuxkcc --build=noexceptions
to build ROOT without exception handling, or set env var EXCEPTIONS=no.
Also reflected in root-config --has-exceptions and --clfags.


git-svn-id: http://root.cern.ch/svn/root/trunk@4333 27541ba8-7e3a-0410-8455-c3a389f83636