Sort files list in lib/Headers/CMakeLists.txt

majnemer pointed out that vadefs.h was added in the wrong place. Might
as well sort the rest too.
clang-cl: Diagnose the usage of ASAN with a debug runtime library

Summary:
AddressSanitizer currently doesn't support this configuration, and binaries
built with it will just get into an infinite loop during startup.

Test Plan: Includes an automated test.

Reviewers: samsonov

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5764