Made the expression parser more resilient against
being asked about symbols it doesn't know about.  If
it's asked about a symbol by mangled name and it finds
nothing, then it will try again with the demangled
base name.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@221660 91177308-0d34-0410-b5e6-96231b3b80d8