A brute-force script for automatic removal of superfluous includes from .cpp files

[geneotech]

• Motivation: To speed up build times even more.
• Input: a list of source files.
  • Could be easily specified with the ones we already specify in CMakeLists.txt, and passed to add_custom_target, named remove_superfluous_includes.
• Approach: brute-force. I propose this algorithm:
  • For every input cpp file, comment out the n-th found include directive by prepending //.
    • Just match against ^#include.
  • Build the project as usual - the script can just call ninja all on a build directory passed as input.
  • Parse the error log to know which sources failed to build.
    • In the ones that failed, uncomment the just commented out include directive (literally just remove the first two characters).
  • (Optional) - build the project once again to ensure that everything is alright.
    • If not, halt and spout a beautiful error.
  • If no file has an (n+1)-th include directive, halt with success.
  • Otherwise repeat the algorithm with n = n + 1.
• While we could simply anaylze each file one-by-one, we would then have to parallelize it by hand.
  • Instead we take advantage of the regular parallelism of builds.
  • As a bonus we actually get to know if the whole project builds.
  • Additionally, if we parallelized on file-level, we would have more i/o overhead due to necessary temporary file copies.
• Problem: with #ifdef-ed code, shit may hit the fan when the defines change.
  • We'll just run it with all defines enabled.
  • We'll just remove platform-specific code and run it specifically on the game code - these should be alright.