fsck: split out fsck return code definitions into a header file of its own

This way we can make use of it from other components too, such as
systemd-homed.

src/shared/fsck-util.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+/* exit codes as defined in fsck(8) */
+enum {
+        FSCK_SUCCESS                 = 0,
+        FSCK_ERROR_CORRECTED         = 1 << 0,
+        FSCK_SYSTEM_SHOULD_REBOOT    = 1 << 1,
+        FSCK_ERRORS_LEFT_UNCORRECTED = 1 << 2,
+        FSCK_OPERATIONAL_ERROR       = 1 << 3,
+        FSCK_USAGE_OR_SYNTAX_ERROR   = 1 << 4,
+        FSCK_USER_CANCELLED          = 1 << 5,
+        FSCK_SHARED_LIB_ERROR        = 1 << 7,
+};

src/shared/meson.build

@@ -74,6 +74,7 @@ shared_sources = files('''
         firewall-util.h
         format-table.c
         format-table.h
+        fsck-util.h
         fstab-util.c
         fstab-util.h
         generator.c