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_12 in 8 minutes and 5 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Precheck
passed precheck:debian:sid:amd64 #37206
amd64 docker linux

00:00:14

 
  Build
passed build:centos:centos6:amd64 #37207
amd64 docker linux

00:02:03

passed build:centos:centos7:amd64 #37208
amd64 docker linux

00:02:04

passed build:debian:sid:amd64 #37209
amd64 docker linux

00:01:31

passed build:debian:sid:i386 #37210
i386 docker linux

00:02:56

 
  Test
passed systemtest:centos:centos6:amd64 #37215
amd64 docker linux

00:04:39

passed systemtest:centos:centos7:amd64 #37216
linux amd64 docker

00:04:43

passed systemtest:debian:sid:amd64 #37217
amd64 docker linux

00:04:43

passed systemtest:debian:sid:i386 #37218
i386 docker linux

00:04:52

passed unittest:centos:centos6:amd64 #37211
amd64 docker linux

00:00:55

passed unittest:centos:centos7:amd64 #37212
amd64 docker linux

00:00:51

passed unittest:debian:sid:amd64 #37213
amd64 docker linux

00:00:51

passed unittest:debian:sid:i386 #37214
i386 docker linux

00:00:47