Previously we relied on CMake's compiler detection module to build the
macros for using the deprecated attribute. However, CMake created macros
for pre-C++14 versions of the feature, which do not work in all cases.
Also, we have the need to be able to suppress deprecation warnings when
we are implementing a deprecated thing. Since we have to query compilers
ourself, we might as well figure out if the deprecated attribute we want
is supported.
Worst case is that we won't support deprecation warnings everywhere we
could. That will not create incorrect code and we can always add that
later.
The `VTKM_DEPRECATED` macro allows us to remove (and usually replace)
features from VTK-m in minor releases while still following the conventions
of semantic versioning. The idea is that when we want to remove or replace
a feature, we first mark the old feature as deprecated. The old feature
will continue to work, but compilers that support it will start to issue a
warning that the use is deprecated and should stop being used. The
deprecated features should remain viable until at least the next major
version. At the next major version, deprecated features from the previous
version may be removed.
