[llvm] [cmake] Make CMAKE_BUILD_TYPE=Release the default (PR #174520)

[Tobias Hieta via llvm-commits]

tru wrote:

I don't mind this - for the size of our project I think Release would be the "correct" default until we can figure out if we can reduce the scale of things like debug information. That however is a very long term project.

I guess the downside to this change is that the text explaining the different build modes are not easily accessible anymore. But maybe users that needs to make this change know where to look?

I wish we had some way to know what the users intent was - if they wanted to build LLVM to use - then Release is correct, or if they want to build it to develop - then Debug is probably more correct and they just have to pick a better toolchain that we could guide them into instead.

https://github.com/llvm/llvm-project/pull/174520