swift234

Add SwiftRuntime dtrace provider with probes for retain, release, allocateObject, deallocateObject.

Now if you want to get these dynamic metrics from the runtime all you
need to do is:

1. Configure Swift with -DSWIFT_RUNTIME_ENABLE_DTRACE=YES
2. Run your routine with the command:

sudo dtrace -s ./utils/runtime_statistics.d -c "$MY_COMMAND_LINE"

After your app finishes running, it will dump out the counts. This is a
much more efficient and low maintenance way to get such statistics than
custom instrumenting the code.

Nothing is changed if -DSWIFT_RUNTIME_ENABLE_DTRACE is not set.

Swift SVN r25264