Use system FindSQlite3.cmake

The `FindSQLite3.cmake` is available with CMake since CMake version 3.14 (see e.g. https://cmake.org/cmake/help/latest/module/FindSQLite3.html).
The release of cmake 3.14 release is from March 2019 (whilst the 3.12 release is from November 2018)

Author: albert-github

BUILD.txt

@@ -1,5 +1,5 @@
 Doxygen uses cmake (http://www.cmake.org/) to build executables for various platforms.
-At least cmake version 3.3 is required.
+At least cmake version 3.14 is required.
 
 The first step is to create a build directory where the output should be stored.
 Doxygen can be fully built outside of the source tree.

CMakeLists.txt

@@ -11,7 +11,7 @@
 # Documents produced by Doxygen are derivative works derived from the
 # input used in their production; they are not affected by this license.
 
-cmake_minimum_required(VERSION 3.12)
+cmake_minimum_required(VERSION 3.14)
 project(doxygen)
 
 option(build_wizard    "Build the GUI frontend for doxygen." OFF)

cmake/FindSQLite3.cmake

@@ -37,7 +37,7 @@ following to build the executable:
     \addindex python
 <li>You need \c python (version 2.7 or higher, see https://www.python.org).
 <li>In order to generate a \c Makefile for your platform, you need
-    <a href="https://cmake.org/">cmake</a> version 3.3 or later.
+    <a href="https://cmake.org/">cmake</a> version 3.14 or later.
     \addindex cmake
 </ul>