Add a check for sys/modem.h, needed by termios on HP-UX.
diff --git a/configure.in b/configure.in
index c17ead7..890aae2 100644
--- a/configure.in
+++ b/configure.in
@@ -381,7 +381,7 @@
AC_HEADER_STDC
AC_CHECK_HEADERS(dlfcn.h fcntl.h limits.h locale.h ncurses.h poll.h pthread.h \
signal.h stdarg.h stddef.h stdlib.h thread.h unistd.h utime.h termios.h \
-sys/audioio.h sys/file.h sys/lock.h db_185.h db.h \
+sys/audioio.h sys/file.h sys/lock.h sys/modem.h db_185.h db.h \
sys/param.h sys/select.h sys/socket.h sys/time.h sys/times.h \
sys/un.h sys/utsname.h sys/wait.h pty.h libutil.h \
ndbm.h db1/ndbm.h gdbm/ndbm.h)