Using

gcc -m32 myprog.c

should compile in 32 bit version the file myprog.c.

Unfortunately I get this error:

In file included from /usr/include/stdio.h:27:0,
                 from myprog.c:1:
/usr/include/features.h:374:25: fatal error: sys/cdefs.h: No such file or directory
#include <sys/cdefs.h>

How could I fix this?

If I don't use -m32 it works but uses 64 bit instructions.

To compile 32 bit binaries on 64 bit Linux version, you have to Install libx32gcc development package and 32 bit GNU C Library

try this

sudo apt-get install libx32gcc-4.8-dev

and

sudo apt-get install libc6-dev-i386