fix FreeBSD before 7 building, broken in r2616

auto/include

diff --git a/auto/include b/auto/include
index 4139238..3a047d3 100644
--- a/auto/include
+++ b/auto/include
@@ -16,6 +16,7 @@
 
 cat << END > $NGX_AUTOTEST.c
 
+$NGX_INCLUDE_SYS_PARAM_H
 #include <$ngx_include>
 
 int main() {