Bug 1837242 - Fix the DLL blocklist code for older versions of Windows. r=gstoll, a=dmeehan

While fixing a crash in bug 1733532, we accidentally broke the DLL
blocklist on older versions of Windows (Windows 7, some versions
of Windows 10, and possibly Windows 8 and 8.1). This is currently
preventing us from mitigating crashes with third-party injected DLLs, in
particular the crash incident from bug 1837242. Considering the volumes
involved, let's temporarily reintroduce bug 1733532 to ensure everyone
has a working blocklist, and deal with bug 1733532 later.

Differential Revision: https://phabricator.services.mozilla.com/D182917