In preparation for the deprecation of `stdenv.isX`.
These shorthands are not conducive to cross-compilation because they
hide the platforms.
Darwin might get cross-compilation for which the continued usage of `stdenv.isDarwin` will get in the way
One example of why this is bad and especially affects compiler packages
https://www.github.com/NixOS/nixpkgs/pull/343059
There are too many files to go through manually but a treewide should
get users thinking when they see a `hostPlatform.isX` in a place where it
doesn't make sense.
```
fd --type f "\.nix" | xargs sd --fixed-strings "stdenv.is" "stdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "stdenv'.is" "stdenv'.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "clangStdenv.is" "clangStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "gccStdenv.is" "gccStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "stdenvNoCC.is" "stdenvNoCC.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "inherit (stdenv) is" "inherit (stdenv.hostPlatform) is"
fd --type f "\.nix" | xargs sd --fixed-strings "buildStdenv.is" "buildStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "effectiveStdenv.is" "effectiveStdenv.hostPlatform.is"
fd --type f "\.nix" | xargs sd --fixed-strings "originalStdenv.is" "originalStdenv.hostPlatform.is"
```
/build/source/src/util/audio_stream.cpp: In function 'void S16ChunkToFloat(const s16*, float*, u32)':
/build/source/src/util/audio_stream.cpp:575:47: note: use '-flax-vector-conversions' to permit conversions between vectors with differing element types or numbers of subparts
/build/source/src/util/audio_stream.cpp:575:57: error: cannot convert 'int16x8_t' to '__Int32x4_t'
The build scripts used by upstream require Git commands. Because of this, a
`deepClone` is required by fetchFromGitHub.
However, keeping `.git` directory around is detrimental to determinism.
Because of this, we need to run the Git commands "manually", save their outputs
and finally remove `.git`.
In order to not pollute the `package.nix`, this peculiar source acquisition is
detached to its own file and `callPackage`d.
Before this Jesuitic hack, the aforementioned data were obtained and filled by
human hands...
