VS: Suppress MSBuild default flags not specified by project or user

`Microsoft.Cl.Common.props` adds some `cl` flags by default, but for
CMake they may not match what's produced by command-line generators.
If the `-Zc:wchar_t`, `-Zc:forScope`, and/or `-Zc:inline` flags are
not specified by the project or user, suppress them.

Fixes: #26964