boot: Deduplicate old-style loader entries.

In cases where systemd (and thus bootctl) is updated to a version
including the earlier unique-ID fix, but the corresponding new version
of systemd-boot is not installed to the ESP and run at least once,
the bootloader will report old-style entry IDs cached in the
LoaderEntries EFI variable, while bootctl will report new-style IDs for
the same entries, producing duplicate entries. This commit makes bootctl
compute and retain old-style IDs for non-auto entries so that it can
properly deduplicate entries even if the cache contains old-style IDs.

src/shared/bootspec.h

@@ -21,6 +21,7 @@ typedef enum BootEntryType {
 typedef struct BootEntry {
         BootEntryType type;
         char *id;       /* This is the file basename without extension */
+        char *id_old;   /* Old-style ID, for deduplication purposes. */
         char *path;     /* This is the full path to the drop-in file */
         char *root;     /* The root path in which the drop-in was found, i.e. to which 'kernel', 'efi' and 'initrd' are relative */
         char *title;
@@ -54,9 +55,12 @@ typedef struct BootConfig {
 static inline bool boot_config_has_entry(BootConfig *config, const char *id) {
         size_t j;
 
-        for (j = 0; j < config->n_entries; j++)
-                if (streq(config->entries[j].id, id))
+        for (j = 0; j < config->n_entries; j++) {
+                const char* entry_id_old = config->entries[j].id_old;
+                if (streq(config->entries[j].id, id) ||
+                    (entry_id_old && streq(entry_id_old, id)))
                         return true;
+        }
 
         return false;
 }