update-via-pacman: ensure that Git for Windows' essential packages are installed

The set of Pacman packages required to build Git for Windows' installer/portable
Git/MinGit from scratch need to be installed in the `git-sdk-*` repositories, so
that MinGit or other backports are possible without having to rely on external
Pacman repositories whose contents might have been culled to make more space.

Let's ensure that these packages (which were uninstalled as part of moving
from MINGW64 to UCRT64 because their UCRT64 counterparts were not yet available)
are installed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

update-via-pacman.ps1

@@ -147,5 +147,21 @@ if (!(Test-Path cmd\git.exe -PathType Leaf)) {
   if (!$?) { die "Could not install mingw-w64-git-for-windows-addons" }
 }
 
+# Make sure that Git for Windows' special packages are installed
+$missing = @()
+
+foreach ($name in "cv2pdb", "curl-openssl-alternate", "git-credential-manager", "wintoast", "xpdf-tools") {
+  $pkg = "mingw-w64-ucrt-x86_64-$name"
+  if (-not (Get-ChildItem -Path "var/lib/pacman/local" -Directory -Filter "$pkg-[0-9]*"
+            -ErrorAction SilentlyContinue)) {
+    $missing += $pkg
+  }
+}
+
+if ($missing) {
+  pacman -S --noconfirm @missing
+  if (!?) { die "Could not install $($missing -join ', ')" }
+}
+
 # Wrapping up: re-install mingw-w64-git-extra
 bash -lc "pacman -S --overwrite=\* --noconfirm mingw-w64-ucrt-x86_64-git-extra"