SunPro 5.15 supports `-std=c++14` and several C++14 features.
SunPro 5.14 accepts `-std=c++14` but does not update its definition of
`__cplusplus` or any other macro to distinguish it from `-std=c++11`,
so we need to blacklist a couple features that do work but that we
cannot report for that version. We can still support `cxx_std_14`.
Co-Author: Robert Maynard <robert.maynard@kitware.com>
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