[GSoC] From Baozeng: Add .printIR meta command, printing the llvm::Module.

...eter/cling/include/cling/Interpreter/CompilationOptions.h

interpreter/cling/include/cling/Interpreter/Interpreter.h

interpreter/cling/lib/Interpreter/IRDumper.cpp

interpreter/cling/lib/Interpreter/Interpreter.cpp

interpreter/cling/lib/MetaProcessor/MetaParser.cpp

interpreter/cling/lib/MetaProcessor/MetaParser.h

interpreter/cling/lib/MetaProcessor/MetaSema.cpp

interpreter/cling/lib/MetaProcessor/MetaSema.h