Legacy Allegro 4 will fail to build with CMake 4+

[NHOrus]

CMake 4 raised minimum compatible version to CMake 3.5. Could it be possible to make a minor version that bumps CMake version only?
See https://gitlab.kitware.com/cmake/cmake/-/issues/26698 and https://gitlab.kitware.com/cmake/cmake/-/issues/26613

[IoIxD]

list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")

has to be added to the top of the CMakeLists.txt file. Also, to use this as a subdirectory, i had to replace all instances of CMAKE_SOURCE_DIR with CMAKE_CURRENT_SOURCE_DIR.

I was then able to bump the cmake version to 2.9. Setting it to the 3.0 or above gives us this:

CMake Error at vendored/allegro4/CMakeLists.txt:991 (get_target_property):
  get_target_property() called with non-existent target "jpgalleg".

note also that I compiled with:

cmake .. -DWANT_EXAMPLES=OFF -DWANT_JPGALLEG=OFF