8182299: Enable disabled clang warnings, build on OSX 10 + Xcode 8
8182656: Make the required changes in GC code to build on OSX 10 + Xcode 8
8182657: Make the required changes in Runtime code to build on OSX 10 + Xcode 8
8182658: Make the required changes in Compiler code to build on OSX 10 + Xcode 8
Reviewed-by: jwilhelm, ehelin, phh
Contributed-by: phh <hohensee@amazon.com>, jwilhelm <jesper.wilhelmsson@oracle.com>