Unable to build uml on 64 bit linux

[ubogdan]

I allways get this error
/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/5/libgcc.a when searching for -lgcc
/usr/bin/ld: cannot find -lgcc
/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/5/libgcc_eh.a when searching for -lgcc_eh
/usr/bin/ld: cannot find -lgcc_eh
collect2: error: ld returned 1 exit status
Makefile:929: recipe for target 'vmlinux' failed
make[1]: *** [vmlinux] Error 1
make[1]: Leaving directory '/home/bogdan/tmp/pythia-core/vm/build/linux-4.4.11'
vm/pythia.mk:59: recipe for target 'out/vm/uml' failed

I have libc6-dev-i386 and squashfs-tools installed on os.

I've tried this before runing make. The problem persists
export CFLAGS='-m32'
export CXXFLAGS='-m32'
export LDFLAGS='-m32'

Aparently it require to install gcc-5-multilib by running
apt-get install gcc-5-multilib

Please update documentation.