IntelLLVM: Avoid unnecessary -Qstd=c++11 flag on Windows

Brad Kingrequested to merge
brad.king/cmake:IntelLLVM-msvc-no-cxx11 into master

The IntelLLVM compiler, for compatibility with MSVC on Windows, always runs with support for at least C++14. The -Qstd=c++11 flag just causes a warning that it is unused.

Fixes: #24316 (closed)
Backport: release

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