treewide: Fix Meson CPU names for powerpc CPUs

(cherry picked from commit 6db6190002)

tests/functional/meson.build

@@ -23,6 +23,8 @@ dot = find_program('dot', native : true, required : false)
 
 nix_bin_dir = fs.parent(nix.full_path())
 
+subdir('nix-meson-build-support/default-system-cpu')
+
 test_confdata = {
   'bindir': nix_bin_dir,
   'coreutils': fs.parent(coreutils.full_path()),
@@ -30,7 +32,7 @@ test_confdata = {
   'bash': bash.full_path(),
   'sandbox_shell': busybox.found() ? busybox.full_path() : '',
   'PACKAGE_VERSION': meson.project_version(),
-  'system': host_machine.cpu_family() + '-' + host_machine.system(),
+  'system': nix_system_cpu + '-' + host_machine.system(),
 }
 
 # Just configures `common/vars-and-functions.sh.in`.

tests/functional/nix-meson-build-support

@@ -0,0 +1 @@
+../../nix-meson-build-support

tests/functional/package.nix

@@ -39,6 +39,7 @@ mkMesonDerivation (
 
     workDir = ./.;
     fileset = fileset.unions [
+      ../../nix-meson-build-support
       ../../scripts/nix-profile.sh.in
       ../../.version
       ../../tests/functional