InstallRequiredSystemLibraries: MBCS MFC is optional on VS 12 (#14903)

The MBCS (Multi-Byte Character Set) has been deprecated with VS 2013,
and MSVC no longer ships with an MBCS-version of MFC by default.
However, it can be downloaded as an add-on.

Teach InstallRequiredSystemLibraries to install the MBCS MFC only
for VS < 12 or if it happens to exist on the system.
Merge topic 'InstallRequiredSystemLibraries-vs12-mfc' into next

c0a6646d InstallRequiredSystemLibraries: MBCS MFC is optional on VS 12 (#14903)