basic: Override glibc's sys/param.h header with an empty file

Instead of unconditionally including sys/param.h in
macro-fundamental.h which itself includes a bunch of other unnecessary
headers, let's override it with an empty file to avoid it from overriding
our MAX() macro. We can't make including it an error as it's included (
for seemingly no good reason) by <resolv.h>.

src/basic/include/sys/param.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/* sys/param.h from glibc unconditionally overrides the MIN() and MAX() macros which interferes with our own
+ * MAX() macro. It also includes a bunch of other headers transitively so we don't want to include
+ * sys/param.h in macro-fundamental.h unconditionally. We'd like to make including this file an error but
+ * unfortunately <resolv.h> includes it. However, <resolv.h> doesn't actually make use of anything from
+ * sys/param.h, so we override it with an empty file so it can't mess with our macros. */

src/basic/macro.h

@@ -5,7 +5,6 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <stdbool.h>
-#include <sys/param.h>
 #include <sys/sysmacros.h>
 #include <sys/types.h>
 

src/basic/pidref.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <signal.h>
+
 #include "macro.h"
 #include "memory-util.h"