swift234

[arc] Integrate ImmutablePointerSet{,Factory} into ARC Sequence Opts.

This speeds and reduces memory consumption of test cases with large
CFGs. The specific test case that spawned this fix was a large function
with many dictionary assignments:

public func func_0(dictIn : [String : MyClass]) -> [String : MyClass] {
  var dictOut : [String : MyClass] = [:]
  dictOut["key5000"] = dictIn["key500"]
  dictOut["key5010"] = dictIn["key501"]
  dictOut["key5020"] = dictIn["key502"]
  dictOut["key5030"] = dictIn["key503"]
  dictOut["key5040"] = dictIn["key504"]
  ...
}

This continued for 10k - 20k values.

This commit reduces the compile time by 2.5x and reduces the amount of
memory allocated by ARC by 2.6x (the memory allocation number includes
memory that is subsequently freed).

rdar://24350646