[libc++] [CMake] Link with /nodefaultlibs on Windows

Summary:
This patch attempts to fix the libc++ build/link so that it doesn't use an default C++ libraries on Windows.  This is needed to prevent linking to MSVC's STL library.

Additionally this patch changes libc++ so that it is always linked with the non-debug DLL's (e.g. `/MD`). This is needed so that the test suite can correctly link the same libraries without needing to know which configuration `c++.dll` was linked with.


Reviewers: compnerd, rnk, majnemer, kimgr, awson, halyavin, smeenai

Subscribers: cfe-commits, mgorny

Differential Revision: https://reviews.llvm.org/D28441

llvm-svn: 292001