This is a very simple task and takes less then a minute. Simple run :
$ git clone https://github.com/CyanogenMod/android_system_core -b cm-12.0
$ cd android_system_core
$ gcc -o ~/mkbootimg libmincrypt/*.c mkbootimg/mkbootimg.c -Iinclude
$ gcc -o ~/unpackbootimg libmincrypt/*.c mkbootimg/unpackbootimg.c -Iinclude
$ gcc -o ~/mkbootfs libmincrypt/*.c cpio/mkbootfs.c -Iinclude
The binaries have now been created in your home directory, go and check them out. If you want to repeat this process run :
$ cd android_system_core
$ git pull
$ gcc -o ~/mkbootimg libmincrypt/*.c mkbootimg/mkbootimg.c -Iinclude
$ gcc -o ~/unpackbootimg libmincrypt/*.c mkbootimg/unpackbootimg.c -Iinclude
$ gcc -o ~/mkbootfs libmincrypt/*.c cpio/mkbootfs.c -Iinclude