[llvm] Escape LLVM_TARGETS_TO_BUILD while checking against LLVM_ALL_TARGETS and LLVM_EXPERIMENTAL_TARGETS_TO_BUILD (PR #70885)

[Shoaib Meenai via llvm-commits]

https://github.com/smeenai approved this pull request.

LGTM, thanks! Will you need someone to land this for you?

https://github.com/llvm/llvm-project/pull/70885