[CFG] Set the “loop target” (back edge) for VisitObjCForCollectionStmt loops
[CFG] Set the “loop target” (back edge) for VisitObjCForCollectionStmt loops

Add the back edge info by creating a basic block, marked as loop target. This is
consistent with how other loops are processed, but was omitted from
VisitObjCForCollectionStmt.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@184617 91177308-0d34-0410-b5e6-96231b3b80d8

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