On OS X it appears the mach exception thread and libdispatch queue threads occasionally get the SIGALRM from the itimer. Count those as foreign_thread_samples instead of letting the signal kill the process.
Set up the state necessary to collect samples. We still need to add GC support for walking the sample set, and the compiler needs to register GC roots before safepoints as well. We also need primitives to expose the data to Factor for reporting.
- make allot_object() inline, move slow case to allot_large_object()
- reduce number of conditional branches in megamorphic cache miss handler
- make unbox_array_size() inline, move slow case to unbox_array_size_slow()
- new memset_cell() function uses memset_pattern4/8() on Mac OS X