Instead of letting swift_NSStringToString leak malloced memory, use swift_allocPOD to allocate storage for the converted String, and stash the heap object into the created string.
Swift SVN r7872
swift_allocPOD allocates a heap object capable of holding POD data of some given size and alignment. This will allow 'alloc_box' and 'alloc_array' to lower specially without instantiating do-nothing heap metadata for POD types, as described in <rdar://problem/13129334>. Update the dynamic swift_allocBox entry point to use swift_allocPOD for POD types. This can also be used by other runtime functions that need to allocate reference-counted scratch memory, such as swift_NSStringToString, as noted in <rdar://problem/14646715>.
Swift SVN r7860
