swift234

[runtime-lib] Any Swift mmap /vm_allocate allocations should use a custom tag.

We now have dedicated tags for Swift on Apple operating systems. They are called: VM_MEMORY_SWIFT_RUNTIME and VM_MEMORY_SWIFT_METADATA.
Let's make use of them. This would allow tools like Instruments provide a more detailed analysis and statistics.

For now, we only tag the metadata allocations, as this is the only place where we use mmap at the moment.

rdar://22376248

Swift SVN r32584