Fix BorrowingInstruction.visitEndBorrows to handle borrowed-from

For borrowed-from of a reborrow, the value is the block argument. So we need to
look through the borrowed-from user.

Author: atrick

SwiftCompilerSources/Sources/Optimizer/Utilities/BorrowUtils.swift

@@ -299,7 +299,7 @@ enum BorrowingInstruction : CustomStringConvertible, Hashable {
 extension BorrowingInstruction {
   private func visitEndBorrows(value: Value, _ context: Context, _ visitor: @escaping (Operand) -> WalkResult)
     -> WalkResult {
-    return value.uses.filterUsers(ofType: EndBorrowInst.self).walk {
+    return value.lookThroughBorrowedFromUser.uses.filterUsers(ofType: EndBorrowInst.self).walk {
       visitor($0)
     }
   }