Avoid dependency on uuid.h in MacOSXDYLD

Summary:
r241964 has added a dependency on uuid.h, which (on linux at least) necessitates instalation of a
new package. Since the only thing we need from that file is uuid_t (and this is already defined
in UuidCompatibility.h), we can avoid this dependency by making this include __APPLE__ specific.
If in future, we need more from this library, we can revisit this decision.

Reviewers: jasonmolenda

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D11135

llvm-svn: 242022