tree-wide: Make sure all headers are standalone

Let's make sure all of our headers include everything they require.

src/libsystemd/sd-bus/bus-signature.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include <stdbool.h>
+#include <stddef.h>
 
 bool signature_is_single(const char *s, bool allow_dict_entry);
 bool signature_is_pair(const char *s);

src/libsystemd/sd-bus/bus-socket.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <stdbool.h>
+
 #include "sd-bus.h"
 
 void bus_socket_setup(sd_bus *b);

src/libsystemd/sd-bus/bus-track.h

@@ -1,5 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+typedef struct sd_bus_track sd_bus_track;
+
 void bus_track_dispatch(sd_bus_track *track);
 void bus_track_close(sd_bus_track *track);

src/libsystemd/sd-bus/test-vtable-data.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-/* This is meant to be included in other files, hence no headers */
+#include <stdbool.h>
+
+#include "sd-bus-vtable.h"
 
 struct context {
         bool quit;

src/libsystemd/sd-journal/mmap-cache.h

@@ -6,6 +6,7 @@
 #include <sys/stat.h>
 
 #include "journal-def.h"
+#include "memory-util.h"
 
 typedef struct MMapCache MMapCache;
 typedef struct MMapFileDescriptor MMapFileDescriptor;

src/libsystemd/sd-json/json-internal.h

@@ -2,8 +2,12 @@
 
 #pragma once
 
+#include <stdbool.h>
+
 #include "sd-json.h"
 
+#include "macro.h"
+
 /* This header should include all prototypes only the JSON parser itself and
  * its tests need access to. Normal code consuming the JSON parser should not
  * interface with this. */

src/libsystemd/sd-netlink/netlink-slot.h

@@ -1,8 +1,12 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <stdbool.h>
+
 #include "sd-netlink.h"
 
+#include "netlink-internal.h"
+
 int netlink_slot_allocate(
                 sd_netlink *nl,
                 bool floating,

src/libsystemd/sd-varlink/varlink-idl-util.h

@@ -4,7 +4,7 @@
 #include "sd-varlink.h"
 #include "sd-varlink-idl.h"
 
-#include "macro.h"
+#include "memory-util.h"
 
 int varlink_idl_parse(const char *text, unsigned *ret_line, unsigned *ret_column, sd_varlink_interface **ret);
 sd_varlink_interface* varlink_interface_free(sd_varlink_interface *interface);