Rename def.h to constants.h

The name "def.h" originates from before the rule of "no needless abbreviations"
was established. Let's rename the file to clarify that it contains a collection
of various semi-related constants.

src/core/execute.c

@@ -48,10 +48,10 @@
 #include "cgroup-setup.h"
 #include "chase-symlinks.h"
 #include "chown-recursive.h"
+#include "constants.h"
 #include "cpu-set-util.h"
 #include "creds-util.h"
 #include "data-fd-util.h"
-#include "def.h"
 #include "env-file.h"
 #include "env-util.h"
 #include "errno-list.h"

src/core/main.c

@@ -37,7 +37,7 @@
 #include "crash-handler.h"
 #include "dbus-manager.h"
 #include "dbus.h"
-#include "def.h"
+#include "constants.h"
 #include "dev-setup.h"
 #include "efi-random.h"
 #include "efivars.h"

src/core/manager.c

@@ -30,13 +30,13 @@
 #include "bus-util.h"
 #include "clean-ipc.h"
 #include "clock-util.h"
+#include "constants.h"
 #include "core-varlink.h"
 #include "creds-util.h"
 #include "dbus-job.h"
 #include "dbus-manager.h"
 #include "dbus-unit.h"
 #include "dbus.h"
-#include "def.h"
 #include "dirent-util.h"
 #include "env-util.h"
 #include "escape.h"

src/core/service.c

@@ -13,9 +13,9 @@
 #include "bus-kernel.h"
 #include "bus-util.h"
 #include "chase-symlinks.h"
+#include "constants.h"
 #include "dbus-service.h"
 #include "dbus-unit.h"
-#include "def.h"
 #include "env-util.h"
 #include "escape.h"
 #include "exit-status.h"

src/core/socket.c

@@ -15,10 +15,10 @@
 #include "bus-error.h"
 #include "bus-util.h"
 #include "chase-symlinks.h"
+#include "constants.h"
 #include "copy.h"
 #include "dbus-socket.h"
 #include "dbus-unit.h"
-#include "def.h"
 #include "errno-list.h"
 #include "exit-status.h"
 #include "fd-util.h"