libcompat: Check that HAVE_DECL_SYS_SIGLIST is 0 instead of undefined

Cherry picked from commit 4e872b317ef6d69d3daab1058ddfa7a8940a06a6.

For declarations the autoconf test always defines the preprocessor
symbol to either 0 or 1, contrary to other tests where it's either
undefined or 1.

Closes: #777044
Based-on-patch-by: Alex Potapenko <opotapenko@gmail.com>

debian/changelog

@@ -103,6 +103,9 @@ dpkg (1.18.0) UNRELEASED; urgency=low
       disabled by default. Closes: #760741
   * Do not accept unknown user or group names on «dpkg-statoverride --add».
     Regression introduced in dpkg 1.17.11. Closes: #775124
+  * Check that HAVE_DECL_SYS_SIGLIST is 0 instead of undefined, to fix a
+    build failure on uclibc based systems. Closes: #777044
+    Based on a patch by Alex Potapenko <opotapenko@gmail.com>.
 
   [ Raphaël Hertzog ]
   * Drop myself from Uploaders.

lib/compat/strsignal.c

@@ -28,7 +28,7 @@
 
 #define _(str) gettext(str)
 
-#ifndef HAVE_DECL_SYS_SIGLIST
+#if !HAVE_DECL_SYS_SIGLIST
 const char *const sys_siglist[] = {
 	NULL,		/* 0 */
 	"SIGHUP",	/* 1 */