appveyor: Determine dlls to include in package programmatically

This is done by recursively calling bindump to determine the dependencies
of each binary that is required from each of the executables. Doing this
allows us to avoid hard-coding a list of required DLL files to copy into
the release archives.

.appveyor/UtilityFunctions.ps1

@@ -0,0 +1,39 @@
+# Set-up Visual Studio Command Prompt environment for PowerShell
+pushd "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Tools\"
+cmd /c "VsDevCmd.bat -arch=x64 & set" | foreach {
+    if ($_ -match "=") {
+        $v = $_.split("="); Set-Item -Force -Path "ENV:\$($v[0])" -Value "$($v[1])"
+    }
+}
+popd
+
+function Which ($search_path, $name) {
+    ($search_path).Split(";") | Get-ChildItem -Filter $name | Select -First 1 -Exp FullName
+}
+
+function GetDeps ($search_path, $binary) {
+    ((dumpbin /dependents $binary).Where({ $_ -match "dependencies:"}, "SkipUntil") | Select-String "[^ ]*\.dll").Matches | foreach {
+        Which $search_path $_.Value
+    }
+}
+
+function RecursivelyGetDeps ($search_path, $binary) {
+    $final_deps = @()
+    $deps_to_process = GetDeps $search_path $binary
+    while ($deps_to_process.Count -gt 0) {
+        $current, $deps_to_process = $deps_to_process
+        if ($final_deps -contains $current) { continue }
+
+        # Is this a system dll file?
+        # We use the same algorithm that cmake uses to determine this.
+        if ($current -match "$([regex]::Escape($env:SystemRoot))\\sys") { continue }
+        if ($current -match "$([regex]::Escape($env:WinDir))\\sys") { continue }
+        if ($current -match "\\msvc[^\\]+dll") { continue }
+        if ($current -match "\\api-ms-win-[^\\]+dll") { continue }
+
+        $final_deps += $current
+        $new_deps = GetDeps $search_path $current
+        $deps_to_process += ($new_deps | ?{-not ($final_deps -contains $_)})
+    }
+    return $final_deps
+}