Fixed ValueObject::UpdateValueIfNeeded to keep
track of the checksum of the object so we can
track if it is modified.  This fixes a testcase
(test/expression_command/issue_11588) on OS X.

Patch by Enrico Granata.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@223830 91177308-0d34-0410-b5e6-96231b3b80d8