Make IntelJITEvents and OProfileJIT as optional libraries and add

optional library support to the llvm-build tool:
 - Add new command line parameter to llvm-build: “--enable-optional-libraries”
 - Add handing of new llvm-build library type “OptionalLibrary”
 - Update Cmake and automake build systems to pass correct flags to llvm-build
   based on configuration

Patch by Dan Malea!

llvm-svn: 156319