Move WindowsDYLD to the Plugins/DynamicLoader directory.

Summary:
This commit moves the Windows DyanamicLoader to the common DynamicLoader
directory. This is required to remote debug Windows targets.

This commit also initializes the Windows DYLD plugin in
SystemInitializerCommon (similarly to both POSIX and MacOSX DYLD
plugins) so that we can automatically instantiate this class when
connected to a windows process.

Test Plan: Build.

Reviewers: zturner

Subscribers: lldb-commits, abdulras

Differential Revision: http://reviews.llvm.org/D10882

llvm-svn: 241697