Add a setting to allow users to enable expressions that crash LLDB to show up in crash logs.

<rdar://problem/11549320> 




git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196613 91177308-0d34-0410-b5e6-96231b3b80d8
Do a little more prevention against SBValues getting used after the world has been torn down around them.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196616 91177308-0d34-0410-b5e6-96231b3b80d8