Since this compiler always defines `__cplusplus` to `1` we need to use
`_MSC_VER`, `__INTEL_CXX11_MODE__`, and the feature test macro named
`__cpp_aggregate_nsdmi` to detect C++11 and C++14 modes.

With no `-Qstd=` flag this compiler defaults to C++98 plus a subset of
C++11/C++14 features needed to be compatible with MSVC.  We pretend it
is plain C++98 and add a `-Qstd=` flag whenever needed for C++11 or
above features even if they would happen to be available in MSVC-mode.

Closes: #16384