llvmPackages_13: init at 13.0.0-rc1

[primeos]

Motivation for this change

Required for Chromium M94 (chromiumDev).
TODOs after this PR:

• Forward port these changes to llvmPackages_git
• Check which llvmPackages_12 fixes weren't applied to llvmPackages_git and ping contributors
  • [R] 8dac270 Revert "llvm_12: disable failing 'DebugInfo/X86/vla-multi.ll' on armv7l"
  • [M] 382fdc7 Merge master into staging-next
  • a7c4537 pkgsi686Linux.llvmPackages_12.compiler-rt: fix build
  • [U] 9a761a4 llvmPackages_12: 12.0.0 -> 12.0.1
  • [n.a.] f69522b clang-tools: fix missing extra tools
  • [R] 68bc5b4 llvm_12: disable failing 'DebugInfo/X86/vla-multi.ll' on armv7l
  • [M] dcfc502 Merge master into staging-next
  • cc7740a lldb: python into lib & wrap binary
  • e097f7e lldb: fix python lldb library
  • [M] 6076dbb Merge master into staging-next
  • cf4e1b9 llvmPackages_12.compiler-rt: fix build on darwin
  • 3530837 llvmPackages*.clang: fix linker invocation with LLVMgold plugin
• Ask John Ericson regarding the GNU install dirs patches

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 Relase notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[primeos]

@ofborg build llvmPackages_13