Get SQLite to build

* changed headers
* removed redundant declarations
* ran clang-format
* added sqlite3.mk

third_party/sqlite3/threads.c

@@ -25,10 +25,11 @@
 ** of multiple cores can do so, while also allowing applications to stay
 ** single-threaded if desired.
 */
-#include "sqliteInt.h"
+#include "third_party/sqlite3/sqliteInt.h"
 #if SQLITE_OS_WIN
-#  include "os_win.h"
+#include "third_party/sqlite3/os_win.h"
 #endif
+/* clang-format off */
 
 #if SQLITE_MAX_WORKER_THREADS>0