Fixed Obj-C GC support; fix pthread name

Fixed Obj-C GC support; fix pthread name

Fixed some recent regressions:
- Always call pthread_setname_np. Recent change removed this if > 10.8.
- Always call objc_registerThreadWithCollector(), except if deploying to 10.12 or later, which GC is removed anyway.

NTH: Note, the header in macOS 10.12 documents that the auto-release
feature was removed and "does nothing" since 10.8. The source code
available from 10.8-10.11 clearly shows that the
objc_registerThreadWithCollector call does something so we will leave
it enabled for this version range. More details are needed from Apple
to interpret the meaning of the deprecation message in 10.12.

Closes #210

Signed-off-by: Nathan Hjelm <hjelmn@me.com>