config: Use env instead of code generation

Code generation messes with the actual source directory and makes it
impossible to use tools like clippy without having generated the config
via meson.

src/meson.build

@@ -1,16 +1,6 @@
-configure_file(input: 'config.rs.in', output: 'config.rs', configuration: conf)
-
 build_root = meson.project_build_root()
 source_root = meson.project_source_root()
 
-# Copy the config.rs output to the source directory.
-run_command(
-  'cp',
-  build_root / 'src' / 'config.rs',
-  source_root / 'src' / 'config.rs',
-  check: true,
-)
-
 cargo_options = ['--manifest-path', source_root / 'Cargo.toml']
 cargo_options += ['--target-dir', build_root / 'src']
 
@@ -27,7 +17,13 @@ if gtk4_x11.found()
   cargo_options += ['--features', 'x11']
 endif
 
-cargo_env = {'CARGO_HOME': build_root / 'cargo-home'}
+cargo_env = {
+  'CARGO_HOME': build_root / 'cargo-home',
+  'APP_ID': app_id,
+  'PROFILE': profile,
+  'VERSION': version,
+  'LOCALEDIR': localedir,
+}
 
 cargo_build = custom_target(
   'cargo-build',