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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> I'm sorry to hear that. Reading through https://libcxx.llvm.org/BuildingLibcxx.html now to see if I can make ENABLE_RUNTIMES behave itself under cross compilation. I'm familiar with this in the context of the "bootstrapping" build from the docs, the build clang first one, which drops (most) arguments passed to cmake. Hopefully building runtimes directly doesn't involve that quirk.

Indeed, pointing cmake at `llvm-project/runtimes` and specifying libunwind in ENABLE_RUNTIMES should work pretty much the same as pointing cmake at libunwind directly, just with a bunch of boilerplate centralized.

I agree that it probably would be good to keep the error message explaining this, especially if it otherwise seems to almost work.

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