[llvm] [LLVM][runtimes] Prepopulate `LLVM_BUILTIN_TARGETS` with runtimes values (PR #95554)

[Chris B via llvm-commits]

llvm-beanz wrote:

> I see, so it's related to the CMake configure step when it tries to identify features? I can see that being an issue for really specific checks where the compiler defaults to compiler-rt for its runtime instead of some GNU libs. Still unfortunate that it adds such a large overhead to build times.

To make the point, who has GNU libs at all? I don't in 3 of the 4 configurations I run LLVM's build for.

Yes it is unfortunate, but there are more build configurations than we can reasonably hard code predictions for.

https://github.com/llvm/llvm-project/pull/95554