cmake core dumps in -6 emulation

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

In order to be able to build packages for -6 on a -8 machine, I set up a 
subdirectroy in /var/chroot containing a tar-ed copy of a real -6 machine. 
I then chroot into there with kver -r 6.1_STABLE /bin/sh.

I tried to build icinga2, but I cmake core dumps with this backtrace:
#0  0x000077a602807644 in write () from /usr/lib/libpthread.so.1
#1  0x000077a6018ee079 in __swrite () from /usr/lib/libc.so.12
#2  0x000077a6018ed84b in __sflush () from /usr/lib/libc.so.12
#3  0x000077a6018ed894 in fflush () from /usr/lib/libc.so.12
#4  0x000077a6018ce870 in __vfprintf_unlocked () from /usr/lib/libc.so.12
#5  0x000077a6018d1c68 in vfprintf () from /usr/lib/libc.so.12
#6  0x000077a6018ccdf4 in fprintf () from /usr/lib/libc.so.12
#7  0x000077a60187e660 in verr () from /usr/lib/libc.so.12
#8  0x000077a601860ac0 in err () from /usr/lib/libc.so.12
#9  0x000077a60280c47b in pthread__init () from /usr/lib/libpthread.so.1
#10 0x000077a60184f105 in _libc_init () from /usr/lib/libc.so.12
#11 0x000077a6018389e4 in ?? () from /usr/lib/libc.so.12
#12 0x000077a604d7a6a0 in ?? ()
#13 0x000077a6018344a9 in _init () from /usr/lib/libc.so.12
#14 0x0000000000000000 in ?? ()

Of course, it build on the real -6 machine (being one of the machines I 
developed the package on).

Any ideas?