swift234

[swift-runtime] Use vm_page_mask if we are compiling for an Apple OS.

Thanks to this, we can get rid of these two dirty symbols:
19f0f24e0 __ZZN17MetadataAllocator5allocEmE12pagesizeMask 8
19f0f24e8 __ZGVZN17MetadataAllocator5allocEmE12pagesizeMask 8

This is part of the effort to put the stdlib into a shared cache.

rdar://22375554

Swift SVN r31388