In cases where the Objective-C ivar symbols are stripped out,

expressions that refer to ivars will not work because Clang
emits IR that refers to them to get the ivar offsets. 
However, it is possible to search the runtime for these values.

I have added support for reading the relevant tables to the
Objective-C runtime, and extended ClangExpressionDeclMap to
query that information if and only if it doesn't find the symbols
in the binary.

Also added a testcase.

<rdar://problem/12628122>

llvm-svn: 168018