Detect HAVE_SYS_TYPES_H in lldb

Summary:
After rL368069 I noticed that HAVE_SYS_TYPES_H is not defined in
Platform.h, or anywhere else in lldb. This change fixes that.

Reviewers: labath

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D65822

llvm-svn: 368125