[clang] [clang] Only build static analyzer sources if requested (PR #71653)

[Balazs Benics via cfe-commits]

steakhal wrote:

As a CSA maintainer, I believe having this component optional is valuable just like @whisperity described.
To me, it's not an important subject such that I'd invest time here, but I'm ready to review patches improving the status quo.
What is important here that by default it would still compile CSA; and I believe clang should be shipped including the CSA component, but users should be able to disable it if they want to. Probably this CMake option worked like this in the past, and it's just not really used in an build bots so it rot.

https://github.com/llvm/llvm-project/pull/71653