Without the change the build of `xorg.libXfont` fails as:
> xtrans-1.5.1/include/X11/Xtrans/Xtrans.c: In function '_FontTransSelectTransport':
> xtrans-1.5.1/include/X11/Xtrans/Xtrans.c:165:10: error: 'i' undeclared (first use in this function)
> 165 | for (i = 0; i < PROTOBUFSIZE && protobuf[i] != '\0'; i++)
> | ^
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"
```
According to the manual, libXpm "deals with compressed files by forking an uncompress or gzip process"
and "writes to a piped compress or gzip process".
Before this commit a path to the host version of `uncompress` is provided, but the build picks up the build version of `gzip`,
so the build doesn't fail, but it uses the wrong `gzip`.
This commit adds the correct paths.
Without it the `mpv` build fails as:
...-libXpresent-1.0.1/include/X11/extensions/Xpresent.h:31:10: fatal error: X11/extensions/Xfixes.h: No such file or directory
31 | #include <X11/extensions/Xfixes.h>
| ^~~~~~~~~~~~~~~~~~~~~~~~~
