Fix object format on Windows (thanks Axel for the hint!)

Solves the following error on Windows (as reported on the forum: https://root.cern.ch/phpBB3/viewtopic.php?f=21&t=19033):
[cling]$ int i = 0;
>>> Caught an interpreter exception!
>>> Incompatible object format!

lib/Interpreter/IncrementalExecutor.cpp

@@ -67,6 +67,12 @@ std::unique_ptr<TargetMachine>
   IncrementalExecutor::CreateHostTargetMachine() const {
   // TODO: make this configurable.
   Triple TheTriple(sys::getProcessTriple());
+#ifdef _WIN32
+  /*
+	* MCJIT works on Windows, but currently only through ELF object format.
+	*/
+  TheTriple.setObjectFormat(llvm::Triple::ELF);
+#endif
   std::string Error;
   const Target *TheTarget
     = TargetRegistry::lookupTarget(TheTriple.getTriple(), Error);