[libunwind] [libunwind] Compile the asm as well as the C++ source (PR #86351)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

This build configuration was explicitly made disallowed in 6f17768e11480063f4c2bcbeea559505fee3ea19, with an error message explaining the situation. However that error message was later removed in 0a22dfcb11c05cbd4f654c8ef1868a4bc6085140.

https://github.com/llvm/llvm-project/pull/86351