Build failure on bastard Slackware box.

I have a 20 year old Slackware host. Yes 20 years with the same IP and hostname, just doing updates.

NTPsec fails to build on it. Unsupported you may think, but it has Linux kernel 4.5.3, gcc 4.8.1, glibc 2.19, etc. Two year old tools should not be a problem for NTPsec. The box compilespretty much everything I try to put on it. Except NTPsec.

Even if NTPsec fails, it should at least have a waf test to tell me what I need to update.

Here is the failure:

[ 99/236] Compiling ntpd/ntp_util.c
In file included from /usr/include/sys/prctl.h:22:0,
                 from ../../ntpd/ntp_sandbox.c:21:
/usr/include/linux/prctl.h:134:2: error: unknown type name '__u64'
  __u64 start_code;  /* code section bounds */
  ^
/usr/include/linux/prctl.h:135:2: error: unknown type name '__u64'
  __u64 end_code;
  ^
/usr/include/linux/prctl.h:136:2: error: unknown type name '__u64'
  __u64 start_data;  /* data section bounds */
  ^
/usr/include/linux/prctl.h:137:2: error: unknown type name '__u64'
  __u64 end_data;
  ^
/usr/include/linux/prctl.h:138:2: error: unknown type name '__u64'
  __u64 start_brk;  /* heap for brk() syscall */
  ^
/usr/include/linux/prctl.h:139:2: error: unknown type name '__u64'
  __u64 brk;
  ^
/usr/include/linux/prctl.h:140:2: error: unknown type name '__u64'
  __u64 start_stack;  /* stack starts at */
  ^
/usr/include/linux/prctl.h:141:2: error: unknown type name '__u64'
  __u64 arg_start;  /* command line arguments bounds */
  ^
/usr/include/linux/prctl.h:142:2: error: unknown type name '__u64'
  __u64 arg_end;
  ^
/usr/include/linux/prctl.h:143:2: error: unknown type name '__u64'
  __u64 env_start;  /* environment variables bounds */
  ^
/usr/include/linux/prctl.h:144:2: error: unknown type name '__u64'
  __u64 env_end;
  ^
/usr/include/linux/prctl.h:145:2: error: unknown type name '__u64'
  __u64 *auxv;   /* auxiliary vector */
  ^

Waf: Leaving directory `/u/local/src/NTP/ntpsec/build/main'
Build failed
 -> task in 'libntpd_obj' failed (exit status 1): 
	{task 155630188: c ntp_sandbox.c -> ntp_sandbox.c.1.o}
['/usr/bin/gcc', '-Wall', '-Wextra', '-I/u/local/src/NTP/ntpsec/build', '-I/u/local/src/NTP/ntpsec/include', '-I/u/local/src/NTP/ntpsec/libisc/include', '-I/u/local/src/NTP/ntpsec/libisc/unix/include', '../../ntpd/ntp_sandbox.c', '-c', '-o', '/u/local/src/NTP/ntpsec/build/main/ntpd/ntp_sandbox.c.1.o']

Prolly time to update my gcc, and glibc, to see if that narrows the problem down.