Enabled blocks support in the expression parser.
Note: although it is now possible to declare blocks
and call them inside the same expression, we do not
generate correct block descriptors so these blocks
cannot be passed to functions like dispatch_async.

<rdar://problem/12578656>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@178509 91177308-0d34-0410-b5e6-96231b3b80d8