Improve Compile Times

[devshgraphicsprogramming]

Description

Do everything here except for Unity Builds: https://unicorn-dev.medium.com/speeding-up-the-build-of-c-and-c-projects-453ce85dd0e1

Description of the related problem

Slow machines compile awfully long, makes it annoying to work on Nabla "on the go".

Solution proposal

First fix https://github.com/buildaworldnet/IrrlichtBAW/issues/196 and get 6 PCH and 6 libs.

Then:

• PCH always on, but only make PCH of dependencies, not self
• Compiler Cache on MSVC (we already use ccache)
• Distributed Builds (Incredibuild for MSVC and distcc for clang if we ever take Unix builds seriously)
• C++20 Modules

Finally, either:

• live++
• or https://github.com/RuntimeCompiledCPlusPlus/RuntimeCompiledCPlusPlus