Add MSI custom action for reliable Windows 10 detection

Add MSI custom action for reliable Windows 10 detection

This patch introduces a `FindSystemInfo()` MSI custom action to reliably
detect Windows 10. The MSI built-in properties for Windows version
detection depend on bootstrapper's manifest. We could provide our own
Windows 10 compatible EXE bootstrapper, but that would cover the
Windows 10 detection in the `InstallUISequence` only. The
`InstallExecuteSequence` is launched by msiexec.exe which we cannot
tamper with would still report `VersionNT` as Windows 8 (603).
Acked-by: Jon Kunkee <jkunkee@microsoft.com>
Message-Id: <20181016102627.18676-4-simon@rozman.si>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17763.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>