ARROW-8397: [C++] Fail to compile aggregate_test.cc on Ubuntu 16.04
ARROW-8397: [C++] Fail to compile aggregate_test.cc on Ubuntu 16.04

Closes #6895 from kszucs/ce

Authored-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

cpcloud/arrow,kou/arrow,apache/arrow,kou/arrow,cpcloud/arrow,apache/arrow,kou/arrow,kou/arrow,apache/arrow,icexelloss/arrow,wesm/arrow,laurentgo/arrow,apache/arrow,xhochy/arrow,laurentgo/arrow,cpcloud/arrow,xhochy/arrow,kou/arrow,apache/arrow,icexelloss/arrow,apache/arrow,wesm/arrow,kou/arrow,wesm/arrow,cpcloud/arrow,xhochy/arrow,xhochy/arrow,xhochy/arrow,apache/arrow,wesm/arrow,apache/arrow,cpcloud/arrow,xhochy/arrow,apache/arrow,xhochy/arrow,kou/arrow,apache/arrow,kou/arrow,cpcloud/arrow,xhochy/arrow,laurentgo/arrow,icexelloss/arrow,xhochy/arrow,cpcloud/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,laurentgo/arrow,xhochy/arrow,wesm/arrow,xhochy/arrow,laurentgo/arrow,cpcloud/arrow,xhochy/arrow,apache/arrow,apache/arrow,xhochy/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,kou/arrow,icexelloss/arrow,laurentgo/arrow,cpcloud/arrow,icexelloss/arrow,wesm/arrow,wesm/arrow,kou/arrow,cpcloud/arrow,cpcloud/arrow,laurentgo/arrow,laurentgo/arrow,icexelloss/arrow,kou/arrow,wesm/arrow,apache/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,icexelloss/arrow,kou/arrow,apache/arrow,icexelloss/arrow,icexelloss/arrow,kou/arrow,wesm/arrow,icexelloss/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,laurentgo/arrow,cpcloud/arrow,cpcloud/arrow,icexelloss/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,cpcloud/arrow,wesm/arrow