[clang] [llvm] [CMake] Preserve clang-prebolt (PR #109351)

[Amir Ayupov via cfe-commits]

aaupov wrote:

> @aaupov this happens on AArch64 target, and only with -split-strategy=cdsplit enabled. Changing it to profile2, for example, fixes the issue

Thanks for clarification. I'll drop cdsplit as we never tested it on AArch64. ARM clang-bolt buildbot hasn't picked this change up yet so I didn't get the signal.

https://github.com/llvm/llvm-project/pull/109351