server: Use thr_kill2 syscall to signal threads on FreeBSD.
diff --git a/configure.ac b/configure.ac
index 6b90cd2..64be416 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1287,6 +1287,7 @@
 	strncasecmp \
 	strtold \
 	tcgetattr \
+	thr_kill2 \
 	timegm \
 	usleep \
 	vsnprintf \