minimal reproducer:
osc co openSUSE:Factory/gnustep-libobjc2 
cd $_
osc build --noservice
chroot /var/tmp/build-root/standard-x86_64/
cd /home/abuild/rpmbuild/BUILD/libobjc2-1.8.1
head -n 348 arc.m > t.m
for i in $(seq 4) ; do clang -c t.m 2>/dev/null ; md5sum t.o ; done

Actual Results:
af35c53170b6d118e1e78ed5b8f2529c  t.o
5c1f40dc0874460958b0b05ed3a55f70  t.o
de320e239b0feb5431a889ff187389a9  t.o
de320e239b0feb5431a889ff187389a9  t.o


When running setarch `arch` -R clang to disable ASLR
or leaving out the last function in t.m (e.g. head -n 315 arc.m > t.m)
it does produce consistent results.