fix: use correct makepkg.conf location without silently failing

There was a typo when implementing the new devtools makepkg.conf
location. Unfortunately the code failed silently which made it not be
detected until now.
Fix this by using the correct location as well as switch to a simple
fall-through approach so we can easily fail instead of silently and
invisibly doing the wrong thing leading to false-negative unreproducible
packages.

Fixes 63ce751

repro.in

@@ -496,11 +496,14 @@ else
   pacman --noconfirm --needed -Sddu "$DEVTOOLS_PKG"
 fi
 
-for makepkg_path in /usr/share/devtools/{makepkg-x86_64.conf,makepkg.d/x86_64.conf}; do
-  if [ -f "\$makepkg_path" ]; then
-    cp -v "\$makepkg_path" /mnt/etc/makepkg.conf
-  fi
-done
+if [[ -f /usr/share/devtools/makepkg.conf.d/x86_64.conf ]]; then
+    cp -v /usr/share/devtools/makepkg.conf.d/x86_64.conf /mnt/etc/makepkg.conf
+elif [[ -f /usr/share/devtools/makepkg-x86_64.conf ]]; then
+    cp -v /usr/share/devtools/makepkg-x86_64.conf /mnt/etc/makepkg.conf
+else
+    echo "Failed to find the makepkg.conf location, please report to archlinux-repro"
+    exit 1
+fi
 __END__
     lock_close 9 "$KEYRINGCACHE/$keyring_package.lock"