[lldb] Qualify includes of Properties[Enum].inc files. NFC

Summary:
This is a bit more explicit, and makes it possible to build LLDB without
varying the -I lines per-directory.
(The latter is useful because many build systems only allow this to be
configured per-library, and LLDB is insufficiently layered to be split into
multiple libraries on stricter build systems).

(My comment on D65185 has some more context)

Reviewers: JDevlieghere, labath, chandlerc, jdoerfert

Reviewed By: labath

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D65397

Patch by Sam McCall!

llvm-svn: 367241