mempool didn't work for sizes less than sizeof(void*)

(cherry picked from commit 5dd1beec)
13 jobs for 474-mempool-is-broken-if-object-size-is-below-the-alignment-size-v9_11 in 9 minutes and 41 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Precheck
passed precheck:debian:sid:amd64 #37299
amd64 docker linux

00:00:12

 
  Build
passed build:centos:centos6:amd64 #37300
amd64 docker linux

00:02:39

passed build:centos:centos7:amd64 #37301
amd64 docker linux

00:02:56

passed build:debian:sid:amd64 #37302
amd64 docker linux

00:01:25

passed build:debian:sid:i386 #37303
i386 docker linux

00:03:50

 
  Test
passed systemtest:centos:centos6:amd64 #37308
amd64 docker linux

00:04:36

passed systemtest:centos:centos7:amd64 #37309
amd64 docker linux

00:04:44

passed systemtest:debian:sid:amd64 #37310
amd64 docker linux

00:04:35

passed systemtest:debian:sid:i386 #37311
i386 docker linux

00:05:11

passed unittest:centos:centos6:amd64 #37304
amd64 docker linux

00:01:05

passed unittest:centos:centos7:amd64 #37305
amd64 docker linux

00:01:07

passed unittest:debian:sid:amd64 #37306
amd64 docker linux

00:01:01

passed unittest:debian:sid:i386 #37307
i386 docker linux

00:00:51