CMakeLists.txt does not expose include directories

[Mrkol]

When one adds allegro5 via add_subdirectory to a cmake project, neither does one get the required include directories set as a property on the allegro target (the preferred way), nor does one get a global cmake variable like `allegro_INCLUDE_DIRECTORIES" (the bad, oldschool way).

For now I had to hack my way around this by manually doing
target_include_directories(allegro INTERFACE <main include folder> <build include path for codegen> <list of enabled addon include folders>),
but allegro's cmakelists could and should do this target_include_directories action on its own.
Please consider adding those.

P.S.
This would make using allegro in cmake projects extremely easy via cpm.cmake:

CPMAddPackage("gh:liballeg/allegro5")
...
add_executable(myHelloWorldApp ...)
target_link_libraries(myHelloWorldApp allegro)

while as it is now I had to spend a couple hours hacking my way around the lack of include directory info.

[connorjclark]

I also had trouble because of this (and other reasons). My workaround was pretty lengthy, sharing in case someone might benefit.