command in the Zaptel.h file of interest:

#ifdef __KERNEL__
#include <linux/config.h>
#include <linux/version.h>
#endif


-----------------------------------------------------
PBX:/usr/src/zaptel# make clean ; make install
rm -f torisatool makefw tor2fw.h radfw.h
rm -f ztcfg torisatool makefw ztmonitor ztspeed  zttest fxotune
rm -f *.o ztcfg tzdriver sethdlc sethdlc-new
rm -f zonedata.lo tonezone.lo libtonezone.so.1.0 *.lo
rm -f *.ko *.mod.c .*o.cmd
rm -rf .tmp_versions
rm -f gendigits tones.h
rm -f libtonezone*
rm -f tor2ee
rm -f fxotune
rm -f core
cc -I. -O4 -g -Wall -DBUILDING_TONEZONE    -DSTANDALONE_ZAPATA -DZAPTEL_CONFIG=\"/etc/zaptel.conf\"   -c -o gendigits.o gendigits.c
cc -o gendigits gendigits.o -lm
./gendigits
gcc -I/usr/src/linux-2.4/include -O6 -DMODULE -D__KERNEL__ -DEXPORT_SYMTAB -I/usr/src/linux/drivers/net -Wall -I. -Wstrict-prototypes -fomit-frame-pointer -I/usr/src/linux/drivers/net/wan -I /usr/src/linux/include -I/usr/src/linux/include/net   -DSTANDALONE_ZAPATA -c zaptel.c
In file included from zaptel.c:40:
zconfig.h:9:26: linux/config.h: No such file or directory
zconfig.h:10:27: linux/version.h: No such file or directory
zconfig.h:66:41: missing binary operator before token "("
zaptel.c:42:26: linux/kernel.h: No such file or directory
zaptel.c:43:25: linux/errno.h: No such file or directory
zaptel.c:44:26: linux/module.h: No such file or directory
zaptel.c:45:27: linux/proc_fs.h: No such file or directory
zaptel.c:46:23: linux/pci.h: No such file or directory
zaptel.c:47:24: linux/init.h: No such file or directory
zaptel.c:48:27: linux/version.h: No such file or directory
zaptel.c:49:24: linux/kmod.h: No such file or directory
zaptel.c:56:28: linux/ppp_defs.h: No such file or directory
In file included from zaptel.c:82:
zaptel.h:35:26: linux/config.h: No such file or directory
zaptel.h:36:27: linux/version.h: No such file or directory
zaptel.h:45:22: linux/fs.h: No such file or directory
zaptel.h:47:41: missing binary operator before token "("
In file included from ecdis.h:30,
                 from zaptel.h:51,
                 from zaptel.c:82:
biquad.h:31: error: parse error before "int32_t"
biquad.h:31: warning: no semicolon at end of struct or union
biquad.h:32: warning: type defaults to `int' in declaration of `a1'