Building llvm-10 fails on macOS Monterey (M1/arm64)

[bucanero]

Steps to reproduce (MacBook-Pro-M1.local 21.1.0 Darwin Kernel Version 21.1.0: Wed Oct 13 17:33:24 PDT 2021; root:xnu-8019.41.5~1/RELEASE_ARM64_T8101 arm64):

brew install --build-from-source llvm-hs/llvm/llvm-10

Error:

==> Installing llvm-hs/llvm/llvm-10
==> cmake -G Unix Makefiles .. -DCMAKE_INSTALL_PREFIX=/opt/homebrew/Cellar/llvm-10/10.0.0/lib/llvm-10
==> make
Last 15 lines from /Users/user/Library/Logs/Homebrew/llvm-10/02.make:
-- ios Simulator supported builtin arches: i386;x86_64
-- Using cached valid architectures for ios.
-- ios supported builtin arches: arm64;armv7;armv7k;armv7s
-- Builtin supported architectures: i386;x86_64;x86_64h;armv7;armv7k;armv7s;arm64
CMake Error at projects/compiler-rt/test/builtins/CMakeLists.txt:55 (message):
  Target clang_rt.builtins_arm64_osx does not exist


-- Configuring incomplete, errors occurred!

[tmcdonell]

I need to get access to an apple silicon Mac to update the formula, but do indeed plan to fix this...