Update cmake_minimum_required to 3.5

This supports compilation with cmake-4.0.0.

Fixes:
CMake Error at CMakeLists.txt:23 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

CMakeLists.txt

@@ -20,7 +20,7 @@
 #
 ############################################################################
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.5)
 
 project(BCG729 VERSION 1.1.1 LANGUAGES C)