Clang v9.0.0 does not support ubuntu20.04 for cross-compiling

[who-biz]

In our depends build system, Clang v9.0.0 is not compatible with ubuntu 20.04 host. Presently discerning if this is the cause of our other issues in macOS cross-compilation.

I've locally pulled in llvm 13.0.0, and this breaks boost compilation, due to a miscalculated "GCC" version (clang is apparently masquerading as GCC), which adds -fcoalesce-templates to boost's build config for darwin.

I was able to move past this error (which others have encountered, see: zcash/zcash#4333), by manually modifiying in contrib/depends/work/build/x86_64-apple-darwin11/1_64_0/tools/build/src/tools/darwin.jam and removing this option.

We need a patch for boost written into depends scripts.

[who-biz]

This is not yet resolved upstream at XMR, from looks of it. Zcash has, resolved it, however. Ultimately, they and Bitcoin use depends build systems. Monero’s seems a less-maintained fork of these.