configure.ac: fix <sys/lwp.h> detection for NetBSD

[Austin English]

Also tested on Ubuntu Intrepid, PC-BSD 7.1, and OpenSolaris.

-- 
-Austin
-------------- next part --------------
diff --git a/configure.ac b/configure.ac
index bf5afe9..9b8528e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -325,7 +325,6 @@ AC_CHECK_HEADERS(\
 	sys/ipc.h \
 	sys/limits.h \
 	sys/link.h \
-	sys/lwp.h \
 	sys/mman.h \
 	sys/modem.h \
 	sys/msg.h \
@@ -373,6 +372,23 @@ AC_CHECK_HEADERS([sys/mount.h sys/statfs.h sys/sysctl.h sys/user.h sys/vfs.h],,,
      # include <sys/param.h>
      #endif])
 
+AC_CHECK_HEADERS([sys/signalvar.h],,,
+    [#include <sys/types.h>
+    #include <signal.h>
+    #ifdef HAVE_SYS_SIGNAL_H
+    # include <sys/signal.h>
+    #endif])
+
+AC_CHECK_HEADERS([sys/lwp.h],,,
+    [#include <sys/types.h>
+    #include <signal.h>
+    #ifdef HAVE_SYS_SIGNALVAR_H
+    # include <sys/signalvar.h>
+    #endif
+    #ifdef HAVE_SYS_SIGNAL_H
+    # include <sys/signal.h>
+    #endif])
+
 AC_CHECK_HEADERS(\
 	netinet/ip.h \
 	net/if.h \