swift234

Tail Allocate the array of protocol conformance pointers on init_existential_metatype.

Previously all uses of this instruction used the single element ArrayRef
constructor. The single element ArrayRef constructor does not require any extra
memory. In the case where one does need extra memory, one would need to allocate
the memory for the init_existential_metatype and pass it in. This commit changes
init_existential_metatype to tail allocate the memory for the conformance
pointers and memcpy them in from the array.

Discovered when a SmallVector of protocol conformances resulted in memory
corruption and frustration =--(.

rdar://22302277

Swift SVN r31276