[PATCH] Configure: fix build with -Werror=nonnull

[Piotr Sikora]

# HG changeset patch
# User Piotr Sikora <piotrsikora at google.com>
# Date 1467064804 25200
#      Mon Jun 27 15:00:04 2016 -0700
# Node ID 2c14d7fb1d96c3a1bfb7e22383bef895287bf7d7
# Parent  d452cb27639f714bc43b7f3ede417e3e7f8efdd6
Configure: fix build with -Werror=nonnull.

Signed-off-by: Piotr Sikora <piotrsikora at google.com>

diff -r d452cb27639f -r 2c14d7fb1d96 auto/unix
--- a/auto/unix
+++ b/auto/unix
@@ -260,7 +260,8 @@ ngx_feature_run=no
 ngx_feature_incs="#include <dlfcn.h>"
 ngx_feature_path=
 ngx_feature_libs=
-ngx_feature_test="dlopen(NULL, RTLD_NOW | RTLD_GLOBAL); dlsym(NULL, NULL)"
+ngx_feature_test="dlopen(\"/dev/null\", RTLD_NOW | RTLD_GLOBAL);
+                  dlsym(NULL, \"dummy\")"
 . auto/feature