[llvm] [runtimes] Fix duplicate BUILTINS_CMAKE_ARGS/RUNTIMES_CMAKE_ARGS (PR #160631)

[Shoaib Meenai via llvm-commits]

smeenai wrote:

Yeah, this feels like a situation where we're definitely doing something silly, but there's also probably various places that are inadvertently relying on the silliness, and it's more trouble than it's worth to sort that out IMO. @petrhosek will probably have an opinion as well though.

https://github.com/llvm/llvm-project/pull/160631