Move various files that don't need to be in basic/ to shared/

This doesn't have much effect on the final build, because we link libbasic.a
into libsystemd-shared.so, so in the end, all the object built from basic/
end up in libsystemd-shared. And when the static library is linked into binaries,
any objects that are included in it but are not used are trimmed. Hence, the
size of output artifacts doesn't change:

$ du -sb /var/tmp/inst*
54181861	/var/tmp/inst1    (old)
54207441	/var/tmp/inst1s   (old split-usr)
54182477	/var/tmp/inst2    (new)
54208041	/var/tmp/inst2s   (new split-usr)

(The negligible change in size is because libsystemd-shared.so is bigger
by a few hundred bytes. I guess it's because symbols are named differently
or something like that.)

The effect is on the build process, in particular partial builds. This change
effectively moves the requirements on some build steps toward the leaves of the
dependency tree. Two effects:
- when building items that do not depend on libsystemd-shared, we
  build less stuff for libbasic.a (which wouldn't be used anyway,
  so it's a net win).
- when building items that do depend on libshared, we reduce libbasic.a as a
  synchronization point, possibly allowing better parallelism.

Method:
1. copy list of .h files from src/basic/meson.build to /tmp/basic
2. $ for i in $(grep '.h$' /tmp/basic); do echo $i; git --no-pager grep "include \"$i\"" src/basic/ 'src/lib*' 'src/nss-*' 'src/journal/sd-journal.c' |grep -v "${i%.h}.c";echo ;done | less

1 files changed, 46 insertions, 0 deletions

diff --git a/src/shared/calendarspec.h b/src/shared/calendarspec.h
new file mode 100644
index 0000000000..3bf8a39e1a
--- /dev/null
+++ b/src/shared/calendarspec.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+/* A structure for specifying (possibly repetitive) points in calendar
+ * time, a la cron */
+
+#include <stdbool.h>
+
+#include "time-util.h"
+#include "util.h"
+
+typedef struct CalendarComponent {
+        int start;
+        int stop;
+        int repeat;
+
+        struct CalendarComponent *next;
+} CalendarComponent;
+
+typedef struct CalendarSpec {
+        int weekdays_bits;
+        bool end_of_month;
+        bool utc;
+        int dst;
+        char *timezone;
+
+        CalendarComponent *year;
+        CalendarComponent *month;
+        CalendarComponent *day;
+
+        CalendarComponent *hour;
+        CalendarComponent *minute;
+        CalendarComponent *microsecond;
+} CalendarSpec;
+
+CalendarSpec* calendar_spec_free(CalendarSpec *c);
+
+int calendar_spec_normalize(CalendarSpec *spec);
+bool calendar_spec_valid(CalendarSpec *spec);
+
+int calendar_spec_to_string(const CalendarSpec *spec, char **p);
+int calendar_spec_from_string(const char *p, CalendarSpec **spec);
+
+int calendar_spec_next_usec(const CalendarSpec *spec, usec_t usec, usec_t *next);
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(CalendarSpec*, calendar_spec_free);