It is a makefile called definitions dot MK which resides in build make core folder.
So we can see that there is a lot of functions defined within the definitions totem.
You can consider this as a library for the make build system, so the methods defined within this definition
start MK are being used extensively by other make files.
For example, if you take all Java files under so this function will return all the Java files which
is coming under a particular path.
So this is used extensively across the Aosp.
You simply search for that in the Makefile and find that it's used extensively across the Makefile.
So similarly there are many other methods which are helpful for building and these are used in other
make files with the introduction of Android.
BP.
The number of places where these methods are used is decreased in the newer builds, but in the past
this was used extensively across all the Mac files when Android was using only make build system.
So in short, just keep in mind that a definition stored MK is the place where you can look for methods
which are used by the make build system.