Build fails on CentOS 6 with CFLAGS=-O2

[scop]

Build fails on CentOS 6 (at least x86_64) with CFLAGS=-O2 (gcc-4.4.7, glibc-2.12):

$ CFLAGS="-O2" make
cc -O2 -Wall -Werror -D_GNU_SOURCE -g   -c -o attach.o attach.c
cc1: warnings being treated as errors
attach.c: In function ‘steal_child_pty’:
attach.c:443: error: dereferencing pointer ‘cm’ does break strict-aliasing rules
attach.c:447: error: dereferencing pointer ‘cm’ does break strict-aliasing rules
attach.c:445: error: dereferencing pointer ‘cm’ does break strict-aliasing rules
attach.c:444: error: dereferencing pointer ‘cm’ does break strict-aliasing rules
attach.c:442: note: initialized from here
make: *** [attach.o] Error 1