Don't do the security scope bookmark dance if not in a sandboxed process

No point in doing it in build-time tools like cppumaker which don't
run as sandboxed processes. Just slows them down a lot, while cfprefsd
consumes lots of CPU doing user preference lookups in vain for every
file accessed through the uunxapi functions.

Change-Id: I83e55a8e8d0c4f2c60c60ecad2c831e42c9e5bfd