[llvm] [clang] Disable runtimes testing in C++03 and Clang modules modes (PR #99303)

[Vlad Serebrennikov via llvm-commits]

Endilll wrote:

Good news are that we got 2 more Linux machines very recently, effectively doubling the capacity we had in the morning. If my understanding of our CI is correct, this should be more than enough to resolve the issue. I'm holding this PR until tomorrow.

https://github.com/llvm/llvm-project/pull/99303