WiX: permit building the installer for ARM64

Windows ARM64 support is slowly being bootstrapped, enable the ARM64
installer which differs only in the upgrade code and the architecture
name.

Author: compnerd

platforms/Windows/installer.wxs renamed to platforms/Windows/installer-amd64.wxs

@@ -0,0 +1,25 @@
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:bal="http://wixtoolset.org/schemas/v4/wxs/bal">
+  <Bundle Name="Swift Developer Package for Windows aarch64" Version="$(var.ProductVersion)" Manufacturer="swift.org" UpgradeCode="151d42d9-8877-4b72-ac62-4695243a35c1">
+    <BootstrapperApplication>
+      <bal:WixStandardBootstrapperApplication LicenseUrl="" LogoFile="Resources/swift.png" SuppressOptionsUI="yes" SuppressRepair="no" Theme="hyperlinkLicense" />
+    </BootstrapperApplication>
+
+    <Chain>
+      <?if $(var.RequiredChain) != "" ?>
+      <?foreach MSI in $(var.RequiredChain) ?>
+      <MsiPackage SourceFile="$(var.MSI_LOCATION)\$(var.MSI)" Compressed="yes">
+        <MsiProperty Name="INSTALL_DEBUGINFO" Value="[INSTALL_DEBUGINFO]" />
+      </MsiPackage>
+      <?endforeach?>
+      <?endif?>
+
+      <?if $(var.OptionalChain) != "" ?>
+      <?foreach MSI in $(var.OptionalChain) ?>
+      <MsiPackage SourceFile="$(var.MSI_LOCATION)\$(var.MSI)" Compressed="yes" Visible="yes">
+        <MsiProperty Name="INSTALL_DEBUGINFO" Value="[INSTALL_DEBUGINFO]" />
+      </MsiPackage>
+      <?endforeach?>
+      <?endif?>
+    </Chain>
+  </Bundle>
+</Wix>

platforms/Windows/installer-arm64.wxs

@@ -5,6 +5,9 @@
   </PropertyGroup>
 
   <PropertyGroup>
+    <ProductArchitecture Condition=" '$(ProductArchitecture)' == '' ">amd64</ProductArchitecture>
+    <ProductArchitecture>$(ProductArchitecture)</ProductArchitecture>
+
     <ProductVersion Condition=" '$(ProductVersion)' == '' ">0.0.0</ProductVersion>
     <ProductVersion>$(ProductVersion)</ProductVersion>
 
@@ -31,6 +34,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Compile Include="installer.wxs" />
+    <Compile Include="installer-$(ProductArchitecture).wxs" />
   </ItemGroup>
 </Project>