Test for presence of sysexits.h and set HAVE_SYSEXITS_H if so.  Used
by posixmodule.c.
diff --git a/configure.in b/configure.in
index 3532ead..9ec081a 100644
--- a/configure.in
+++ b/configure.in
@@ -749,7 +749,7 @@
 sys/audioio.h sys/file.h sys/lock.h sys/mkdev.h sys/modem.h \
 sys/param.h sys/poll.h sys/select.h sys/socket.h sys/time.h sys/times.h \
 sys/un.h sys/utsname.h sys/wait.h pty.h term.h libutil.h \
-sys/resource.h netpacket/packet.h)
+sys/resource.h netpacket/packet.h sysexits.h)
 AC_HEADER_DIRENT
 AC_HEADER_MAJOR