CMake: Fix WiX installer downgrades with versioned binaries

Since commit 5b9da05b7a (Windows: Embed version information into CMake
binaries, 2017-10-25, v3.11.0-rc1~411^2) our binaries have version
information that prevents a `.msi` downgrade from replacing them by
default.  Configure the re-install mode:

* a: reinstall all files regardless of version
* m: rewrite all per-machine registry entries
* u: rewrite all per-user registry entries
* s: reinstall shortcuts and icons

Fixes: #19006

Utilities/Release/WiX/WIX.template.in

@@ -20,6 +20,8 @@
             Schedule="afterInstallInitialize"
             AllowDowngrades="yes"/>
 
+        <Property Id="REINSTALLMODE" Value="amus"/>
+
         <WixVariable Id="WixUILicenseRtf" Value="$(var.CPACK_WIX_LICENSE_RTF)"/>
         <Property Id="WIXUI_INSTALLDIR" Value="INSTALL_ROOT"/>