Agg sum with decimal (#4546)

Declaration of supplementary C function

Approved by: @nnsgmsone, @fengttt

cgo/mo.h

@@ -158,6 +158,7 @@ int32_t Logic_VecNot(void *r, void *a, uint64_t n, uint64_t *nulls, int32_t flag
 
 /* aggregation operation */
 int32_t Decimal64_VecSum(int64_t *rs, int64_t *vs, int64_t start, int64_t count, uint64_t *vps ,int64_t *zs, uint64_t *nulls);
+int32_t Decimal64_VecSumToDecimal128(int64_t *rs, int64_t *vs, int64_t start, int64_t count, uint64_t *vps ,int64_t *zs, uint64_t *nulls);
 int32_t Decimal128_VecSum(int64_t *rs, int64_t *vs, int64_t start, int64_t count, uint64_t *vps ,int64_t *zs, uint64_t *nulls);
 
 #endif /* _MO_H_ */