https://bugs.ntp.org/show_bug.cgi?id=3942

--- configure.ac.orig
+++ configure.ac
@@ -300,6 +300,7 @@
 AC_HEADER_STDBOOL
 AC_CHECK_HEADERS([stdlib.h string.h termio.h])
 AC_CHECK_HEADERS([termios.h timepps.h timex.h unistd.h])
+AC_CHECK_HEADERS([sys/syscall.h])
 
 case "$host" in
  *-*-aix*)
@@ -1102,6 +1103,9 @@
 		#ifdef HAVE_UNISTD_H
 		# include <unistd.h>
 		#endif
+		#ifdef HAVE_SYS_SYSCALL_H
+		# include <sys/syscall.h>
+		#endif
 	    ]],
 	    [[
 		extern int syscall (int, ...);