buildFHSEnv: add multiArch flag

The intention is to allow the user control over whether 32bit deps are supposed
to be included in the fhsenv

doc/builders/special/fhs-environments.section.md

@@ -11,6 +11,8 @@ Accepted arguments are:
         Packages to be installed for the main host's architecture (i.e. x86_64 on x86_64 installations). Along with libraries binaries are also installed.
 - `multiPkgs`
         Packages to be installed for all architectures supported by a host (i.e. i686 and x86_64 on x86_64 installations). Only libraries are installed by default.
+- `multiArch`
+        Whether to install 32bit multiPkgs into the FHSEnv in 64bit environments
 - `extraBuildCommands`
         Additional commands to be executed for finalizing the directory structure.
 - `extraBuildCommandsMulti`

pkgs/build-support/build-fhsenv-bubblewrap/buildFHSEnv.nix

@@ -12,6 +12,7 @@
 , profile ? ""
 , targetPkgs ? pkgs: []
 , multiPkgs ? pkgs: []
+, multiArch ? true # Whether to include 32bit packages
 , extraBuildCommands ? ""
 , extraBuildCommandsMulti ? ""
 , extraOutputsToInstall ? []
@@ -35,8 +36,8 @@
 let
   inherit (stdenv) is64bit;
 
-  # use of glibc_multi is only supported on x86_64-linux
-  isMultiBuild = stdenv.system == "x86_64-linux";
+  # "use of glibc_multi is only supported on x86_64-linux"
+  isMultiBuild = multiArch && stdenv.system == "x86_64-linux";
   isTargetBuild = !isMultiBuild;
 
   # list of packages (usually programs) which are only be installed for the