Kept separate from 2c627d9 to skip CI for this trivial change.

(cherry picked from commit 46d395e)

(cherry picked from commit d4c2564)

(cherry picked from commit 3c7fba2)

(cherry picked from commit fd155c2)

(cherry picked from commit c672de3)
Reason: This is required for llvmPackages_16 (and llvmPackages_15). Only
if stdenv.hostPlatform.isFreeBSD but backporting new packages is fine
and so that everything evaluates without errors.

This code is backported from nixos-unstable (2c627d9) and the power
platform isn't defined/supported on NixOS 22.11 yet, e.g.:
```
$ nix-instantiate -A llvmPackages_16
error: attribute 'power' missing

       at /home/michael/nixpkgs/worktrees/22.11/pkgs/development/compilers/llvm/16/default.nix:96:7:

           95|       lib.platforms.mips ++
           96|       lib.platforms.power ++
             |       ^
           97|       lib.platforms.riscv ++
(use '--show-trace' to show detailed location information)
```

This comes from eb2eafd (or rather [0]). I only backported the
patch instead of the whole commit to avoid mass rebuilds for
llvmPackages 13 and 14 (there is a small diff in the patches due to the
headers ("index" and the line numbers)).

This fixes:
```
error (ignored): error: end of string reached
error: getting status of 'pkgs/development/compilers/llvm/common/clang/add-nostdlibinc-flag.patch': No such file or directory
```

[0]: pkgs/development/compilers/llvm/git/clang/add-nostdlibinc-flag.patch

This code is backported from nixos-unstable (2c627d9) and isn't
fully compatible with NixOS 22.11 due to other missing
abstractions/changes. I simply went with the exact same code as the
other llvmPackages already use here. This fixes the following error:
```
error: cannot coerce a set to a string

        at pkgs/development/compilers/llvm/16/compiler-rt/default.nix:34:3:

            33|
            34|   env.NIX_CFLAGS_COMPILE = toString [
              |   ^
            35|     "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
```