Fix expression parsing (on FreeBSD, at least)

This reverts part of r204112 (Expression: cleanup unused include).
It looks like MCJIT.h is required to force MCJIT to be linked.

llvm-svn: 204170
diff --git a/lldb/source/Expression/ClangExpressionParser.cpp b/lldb/source/Expression/ClangExpressionParser.cpp
index 4c5ebd1..46623c0 100644
--- a/lldb/source/Expression/ClangExpressionParser.cpp
+++ b/lldb/source/Expression/ClangExpressionParser.cpp
@@ -55,6 +55,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/TargetSelect.h"
 
+#include "llvm/ExecutionEngine/MCJIT.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/ErrorHandling.h"