Add low-impact warning flags, fix warnings found by new flags

Add compiler flags: -Wundef, -Wfloat-equal, -Wredundant-decls, -Walloc-zero.

Fix -Wredundant-decls warnings:
- Remove stale cons_show_desktop_prefs declaration (ui.h)
- Remove duplicate connection_set_priority prototype (connection.h)
- Remove stale omemo_devicelist_configure_and_request declaration (omemo.h)

Fix potential buffer overflow in stanza.c:
- Increase pri_str and idle_str buffers from 10 to 12 bytes
  (INT_MIN = -2147483648 needs 12 bytes including NUL)

src/database.c

@@ -168,21 +168,21 @@ log_database_init(ProfAccount* account)
     // replaces_db_id is ID (primary key) of the original message that LMC message corrects/replaces
     // replaced_by_db_id is ID (primary key) of the last correcting (LMC) message for the original message
     const char* query = "CREATE TABLE IF NOT EXISTS `ChatLogs` ("
-                  "`id` INTEGER PRIMARY KEY AUTOINCREMENT, "
-                  "`from_jid` TEXT NOT NULL, "
-                  "`to_jid` TEXT NOT NULL, "
-                  "`from_resource` TEXT, "
-                  "`to_resource` TEXT, "
-                  "`message` TEXT, "
-                  "`timestamp` TEXT, "
-                  "`type` TEXT, "
-                  "`stanza_id` TEXT, "
-                  "`archive_id` TEXT, "
-                  "`encryption` TEXT, "
-                  "`marked_read` INTEGER, "
-                  "`replace_id` TEXT, "
-                  "`replaces_db_id` INTEGER, "
-                  "`replaced_by_db_id` INTEGER)";
+                        "`id` INTEGER PRIMARY KEY AUTOINCREMENT, "
+                        "`from_jid` TEXT NOT NULL, "
+                        "`to_jid` TEXT NOT NULL, "
+                        "`from_resource` TEXT, "
+                        "`to_resource` TEXT, "
+                        "`message` TEXT, "
+                        "`timestamp` TEXT, "
+                        "`type` TEXT, "
+                        "`stanza_id` TEXT, "
+                        "`archive_id` TEXT, "
+                        "`encryption` TEXT, "
+                        "`marked_read` INTEGER, "
+                        "`replace_id` TEXT, "
+                        "`replaces_db_id` INTEGER, "
+                        "`replaced_by_db_id` INTEGER)";
     if (SQLITE_OK != sqlite3_exec(g_chatlog_database, query, NULL, 0, &err_msg)) {
         goto out;
     }