pypaBuildHook: handle pypaBuildFlags __structuredAttrs-agnostically

pkgs/development/interpreters/python/hooks/pypa-build-hook.sh

@@ -5,8 +5,16 @@ pypaBuildPhase() {
     echo "Executing pypaBuildPhase"
     runHook preBuild
 
+    local -a flagsArray=(
+        --no-isolation
+        --outdir dist/
+        --wheel
+    )
+    concatTo flagsArray pypaBuildFlags
+
     echo "Creating a wheel..."
-    @build@/bin/pyproject-build --no-isolation --outdir dist/ --wheel $pypaBuildFlags
+    echoCmd 'pypa build flags' "${flagsArray[@]}"
+    @build@/bin/pyproject-build "${flagsArray[@]}"
     echo "Finished creating a wheel..."
 
     runHook postBuild

pkgs/development/python-modules/meson-python/add-build-flags.sh

@@ -1,7 +1,7 @@
 mesonPythonBuildFlagsHook() {
   # Add all of mesonFlags to -Csetup-args for pypa builds
   for f in $mesonFlags; do
-    pypaBuildFlags+=" -Csetup-args=$f"
+    appendToVar pypaBuildFlags "-Csetup-args=$f"
     # This requires pip>23.0.1, see: https://meson-python.readthedocs.io/en/latest/how-to-guides/config-settings.html
     appendToVar pipBuildFlags "--config-settings=setup-args=$f"
   done