build-sys: make the dynamic UID range, and the container UID range configurable

Also, export these ranges in our pkg-config files.

src/nspawn/nspawn-def.h

@@ -21,12 +21,6 @@
 
 #include <sys/types.h>
 
-/* Note that devpts's gid= parameter parses GIDs as signed values, hence we stay away from the upper half of the 32bit
- * UID range here. We leave a bit of room at the lower end and a lot of room at the upper end, so that other subsystems
- * may have their own allocation ranges too. */
-#define UID_SHIFT_PICK_MIN ((uid_t) UINT32_C(0x00080000))
-#define UID_SHIFT_PICK_MAX ((uid_t) UINT32_C(0x6FFF0000))
-
 /* While we are chmod()ing a directory tree, we set the top-level UID base to this "busy" base, so that we can always
  * recognize trees we are were chmod()ing recursively and got interrupted in */
 #define UID_BUSY_BASE ((uid_t) UINT32_C(0xFFFE0000))

src/nspawn/nspawn.c

@@ -2862,7 +2862,7 @@ static int uid_shift_pick(uid_t *shift, LockFile *ret_lock_file) {
                 if (--n_tries <= 0)
                         return -EBUSY;
 
-                if (candidate < UID_SHIFT_PICK_MIN || candidate > UID_SHIFT_PICK_MAX)
+                if (candidate < CONTAINER_UID_BASE_MIN || candidate > CONTAINER_UID_BASE_MAX)
                         goto next;
                 if ((candidate & UINT32_C(0xFFFF)) != 0)
                         goto next;
@@ -2904,7 +2904,7 @@ static int uid_shift_pick(uid_t *shift, LockFile *ret_lock_file) {
                 } else
                         random_bytes(&candidate, sizeof(candidate));
 
-                candidate = (candidate % (UID_SHIFT_PICK_MAX - UID_SHIFT_PICK_MIN)) + UID_SHIFT_PICK_MIN;
+                candidate = (candidate % (CONTAINER_UID_BASE_MAX - CONTAINER_UID_BASE_MIN)) + CONTAINER_UID_BASE_MIN;
                 candidate &= (uid_t) UINT32_C(0xFFFF0000);
         }
 }