When I added the use of the new compression framework (present in

Mac OS X 10.11, El Capitan, released c. Oct 2015) I conditionalized
the use of the framework on "if sdk == macosx 10.11".  But since
macOS 10.12 has shipped this year, the framework was no longer being
built in.  I can either start listing every OS 10.11 and newer, or
remove the version check.

This will break building lldb with xcodebuild / Xcode for people 
running Mac OS X 10.10 or older.  If so, I'll back this change out.
I'm not sure if we have many people working on macs running the
older OSes on their build systems.

<rdar://problem/30159130> 

llvm-svn: 293742