Fix five of the shared library build targets

Before this patch there was a cyclic dependency between lldCore and
lldReaderWriter.  Only lldConfig could be built as a shared library.

* Moved Reader and Writer base classes into lldCore.
* The following shared libraries can now be built:
     lldCore
     lldYAML
     lldNative
     lldPasses
     lldReaderWriter

Differential Revision: http://reviews.llvm.org/D7105

From: Greg Fitzgerald <garious@gmail.com>
llvm-svn: 226732