meson: Optimize add-wants targets

Instead of invoking meson-add-wants.sh once for each wants that has
to be added, we pass all wants to a single invocation of
meson-add-wants.sh and in meson-add-wants.sh, loop over the
arguments.

This saves about 300ms on the install step.

Before:

```
‣ Running build script...
[1/418] Generating version.h with a custom command
Installing /root/build/po/be.gmo to /root/dest/usr/share/locale/be/LC_MESSAGES/systemd.mo
Installing /root/build/po/be@latin.gmo to /root/dest/usr/share/locale/be@latin/LC_MESSAGES/systemd.mo
Installing /root/build/po/bg.gmo to /root/dest/usr/share/locale/bg/LC_MESSAGES/systemd.mo
Installing /root/build/po/ca.gmo to /root/dest/usr/share/locale/ca/LC_MESSAGES/systemd.mo
Installing /root/build/po/cs.gmo to /root/dest/usr/share/locale/cs/LC_MESSAGES/systemd.mo
Installing /root/build/po/da.gmo to /root/dest/usr/share/locale/da/LC_MESSAGES/systemd.mo
Installing /root/build/po/de.gmo to /root/dest/usr/share/locale/de/LC_MESSAGES/systemd.mo
Installing /root/build/po/el.gmo to /root/dest/usr/share/locale/el/LC_MESSAGES/systemd.mo
Installing /root/build/po/es.gmo to /root/dest/usr/share/locale/es/LC_MESSAGES/systemd.mo
Installing /root/build/po/fr.gmo to /root/dest/usr/share/locale/fr/LC_MESSAGES/systemd.mo
Installing /root/build/po/gl.gmo to /root/dest/usr/share/locale/gl/LC_MESSAGES/systemd.mo
Installing /root/build/po/hr.gmo to /root/dest/usr/share/locale/hr/LC_MESSAGES/systemd.mo
Installing /root/build/po/hu.gmo to /root/dest/usr/share/locale/hu/LC_MESSAGES/systemd.mo
Installing /root/build/po/id.gmo to /root/dest/usr/share/locale/id/LC_MESSAGES/systemd.mo
Installing /root/build/po/it.gmo to /root/dest/usr/share/locale/it/LC_MESSAGES/systemd.mo
Installing /root/build/po/ja.gmo to /root/dest/usr/share/locale/ja/LC_MESSAGES/systemd.mo
Installing /root/build/po/ko.gmo to /root/dest/usr/share/locale/ko/LC_MESSAGES/systemd.mo
Installing /root/build/po/lt.gmo to /root/dest/usr/share/locale/lt/LC_MESSAGES/systemd.mo
Installing /root/build/po/pl.gmo to /root/dest/usr/share/locale/pl/LC_MESSAGES/systemd.mo
Installing /root/build/po/pt_BR.gmo to /root/dest/usr/share/locale/pt_BR/LC_MESSAGES/systemd.mo
Installing /root/build/po/ro.gmo to /root/dest/usr/share/locale/ro/LC_MESSAGES/systemd.mo
Installing /root/build/po/ru.gmo to /root/dest/usr/share/locale/ru/LC_MESSAGES/systemd.mo
Installing /root/build/po/sk.gmo to /root/dest/usr/share/locale/sk/LC_MESSAGES/systemd.mo
Installing /root/build/po/sr.gmo to /root/dest/usr/share/locale/sr/LC_MESSAGES/systemd.mo
Installing /root/build/po/sv.gmo to /root/dest/usr/share/locale/sv/LC_MESSAGES/systemd.mo
Installing /root/build/po/tr.gmo to /root/dest/usr/share/locale/tr/LC_MESSAGES/systemd.mo
Installing /root/build/po/uk.gmo to /root/dest/usr/share/locale/uk/LC_MESSAGES/systemd.mo
Installing /root/build/po/zh_CN.gmo to /root/dest/usr/share/locale/zh_CN/LC_MESSAGES/systemd.mo
Installing /root/build/po/zh_TW.gmo to /root/dest/usr/share/locale/zh_TW/LC_MESSAGES/systemd.mo
Installing /root/build/po/pa.gmo to /root/dest/usr/share/locale/pa/LC_MESSAGES/systemd.mo

real    0m1.465s
user    0m1.025s
sys     0m0.426s
```

After:

```
‣ Running build script...
[1/418] Generating version.h with a custom command
Installing /root/build/po/be.gmo to /root/dest/usr/share/locale/be/LC_MESSAGES/systemd.mo
Installing /root/build/po/be@latin.gmo to /root/dest/usr/share/locale/be@latin/LC_MESSAGES/systemd.mo
Installing /root/build/po/bg.gmo to /root/dest/usr/share/locale/bg/LC_MESSAGES/systemd.mo
Installing /root/build/po/ca.gmo to /root/dest/usr/share/locale/ca/LC_MESSAGES/systemd.mo
Installing /root/build/po/cs.gmo to /root/dest/usr/share/locale/cs/LC_MESSAGES/systemd.mo
Installing /root/build/po/da.gmo to /root/dest/usr/share/locale/da/LC_MESSAGES/systemd.mo
Installing /root/build/po/de.gmo to /root/dest/usr/share/locale/de/LC_MESSAGES/systemd.mo
Installing /root/build/po/el.gmo to /root/dest/usr/share/locale/el/LC_MESSAGES/systemd.mo
Installing /root/build/po/es.gmo to /root/dest/usr/share/locale/es/LC_MESSAGES/systemd.mo
Installing /root/build/po/fr.gmo to /root/dest/usr/share/locale/fr/LC_MESSAGES/systemd.mo
Installing /root/build/po/gl.gmo to /root/dest/usr/share/locale/gl/LC_MESSAGES/systemd.mo
Installing /root/build/po/hr.gmo to /root/dest/usr/share/locale/hr/LC_MESSAGES/systemd.mo
Installing /root/build/po/hu.gmo to /root/dest/usr/share/locale/hu/LC_MESSAGES/systemd.mo
Installing /root/build/po/id.gmo to /root/dest/usr/share/locale/id/LC_MESSAGES/systemd.mo
Installing /root/build/po/it.gmo to /root/dest/usr/share/locale/it/LC_MESSAGES/systemd.mo
Installing /root/build/po/ja.gmo to /root/dest/usr/share/locale/ja/LC_MESSAGES/systemd.mo
Installing /root/build/po/ko.gmo to /root/dest/usr/share/locale/ko/LC_MESSAGES/systemd.mo
Installing /root/build/po/lt.gmo to /root/dest/usr/share/locale/lt/LC_MESSAGES/systemd.mo
Installing /root/build/po/pl.gmo to /root/dest/usr/share/locale/pl/LC_MESSAGES/systemd.mo
Installing /root/build/po/pt_BR.gmo to /root/dest/usr/share/locale/pt_BR/LC_MESSAGES/systemd.mo
Installing /root/build/po/ro.gmo to /root/dest/usr/share/locale/ro/LC_MESSAGES/systemd.mo
Installing /root/build/po/ru.gmo to /root/dest/usr/share/locale/ru/LC_MESSAGES/systemd.mo
Installing /root/build/po/sk.gmo to /root/dest/usr/share/locale/sk/LC_MESSAGES/systemd.mo
Installing /root/build/po/sr.gmo to /root/dest/usr/share/locale/sr/LC_MESSAGES/systemd.mo
Installing /root/build/po/sv.gmo to /root/dest/usr/share/locale/sv/LC_MESSAGES/systemd.mo
Installing /root/build/po/tr.gmo to /root/dest/usr/share/locale/tr/LC_MESSAGES/systemd.mo
Installing /root/build/po/uk.gmo to /root/dest/usr/share/locale/uk/LC_MESSAGES/systemd.mo
Installing /root/build/po/zh_CN.gmo to /root/dest/usr/share/locale/zh_CN/LC_MESSAGES/systemd.mo
Installing /root/build/po/zh_TW.gmo to /root/dest/usr/share/locale/zh_TW/LC_MESSAGES/systemd.mo
Installing /root/build/po/pa.gmo to /root/dest/usr/share/locale/pa/LC_MESSAGES/systemd.mo

real    0m1.162s
user    0m0.803s
sys     0m0.338s
```

2 files changed, 38 insertions, 30 deletions

diff --git a/units/meson-add-wants.sh b/units/meson-add-wants.sh
index 2241fc26a2..b7f57a5e2c 100755
--- a/units/meson-add-wants.sh
+++ b/units/meson-add-wants.sh
@@ -1,34 +1,39 @@
 #!/bin/sh
 set -eu
 
-unitdir="$1"
-target="$2"
-unit="$3"
+i=1
+while [ $i -lt $# ] ; do
+    eval unitdir="\${$i}"
+    eval target="\${$((i + 1))}"
+    eval unit="\${$((i + 2))}"
 
-if [ "${MESON_INSTALL_QUIET:-0}" = 1 ] ; then
-    VERBOSE=""
-else
-    VERBOSE="v"
-fi
+    if [ "${MESON_INSTALL_QUIET:-0}" = 1 ] ; then
+        VERBOSE=""
+    else
+        VERBOSE="v"
+    fi
 
-case "$target" in
-    */?*) # a path, but not just a slash at the end
-        dir="${DESTDIR:-}${target}"
-        ;;
-    *)
-        dir="${DESTDIR:-}${unitdir}/${target}"
-        ;;
-esac
+    case "$target" in
+        */?*) # a path, but not just a slash at the end
+            dir="${DESTDIR:-}${target}"
+            ;;
+        *)
+            dir="${DESTDIR:-}${unitdir}/${target}"
+            ;;
+    esac
 
-unitpath="${DESTDIR:-}${unitdir}/${unit}"
+    unitpath="${DESTDIR:-}${unitdir}/${unit}"
 
-case "$target" in
-    */)
-        mkdir -${VERBOSE}p -m 0755 "$dir"
-        ;;
-    *)
-        mkdir -${VERBOSE}p -m 0755 "$(dirname "$dir")"
-        ;;
-esac
+    case "$target" in
+        */)
+            mkdir -${VERBOSE}p -m 0755 "$dir"
+            ;;
+        *)
+            mkdir -${VERBOSE}p -m 0755 "$(dirname "$dir")"
+            ;;
+    esac
 
-ln -${VERBOSE}fs --relative "$unitpath" "$dir"
+    ln -${VERBOSE}fs --relative "$unitpath" "$dir"
+
+    i=$((i + 3))
+done
diff --git a/units/meson.build b/units/meson.build
index ba60eb7fc1..8b8fd1173f 100644
--- a/units/meson.build
+++ b/units/meson.build
@@ -247,6 +247,8 @@ m4_units = [
         ['serial-getty@.service',              ''],
 ]
 
+add_wants = []
+
 foreach tuple : in_units
         file = tuple[0]
 
@@ -270,7 +272,7 @@ foreach tuple : in_units
 
         if install and tuple.length() > 2
                 foreach target : tuple[2].split()
-                        meson.add_install_script('meson-add-wants.sh', systemunitdir, target, file)
+                        add_wants += [systemunitdir, target, file]
                 endforeach
         endif
 endforeach
@@ -295,7 +297,7 @@ foreach tuple : m4_units
 
         if tuple.length() > 2 and install
                 foreach target : tuple[2].split()
-                        meson.add_install_script('meson-add-wants.sh', systemunitdir, target, file)
+                        add_wants += [systemunitdir, target, file]
                 endforeach
         endif
 endforeach
@@ -314,13 +316,14 @@ foreach tuple : units
 
                 if tuple.length() > 2
                         foreach target : tuple[2].split()
-                                meson.add_install_script(
-                                        'meson-add-wants.sh', systemunitdir, target, file)
+                                add_wants += [systemunitdir, target, file]
                         endforeach
                 endif
         endif
 endforeach
 
+meson.add_install_script('meson-add-wants.sh', add_wants)
+
 install_data('user-.slice.d/10-defaults.conf',
              install_dir : systemunitdir + '/user-.slice.d')