DCMTK

Implement CMake test for the various C++ deprecation attributes and implement an "OFdeprecated" macro that is resolved to

• [[deprecated]] if supported (see https://en.cppreference.com/w/cpp/language/attributes/deprecated, C++14 feature)
• __declspec(deprecated) on Visual Studio (supported since Visual Studio 2003) (see https://docs.microsoft.com/de-de/cpp/cpp/deprecated-cpp?view=vs-2019)
• __attribute__((deprecated)) on gcc (supported since gcc 3.0) and clang (see https://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Type-Attributes.html#Type-Attributes and http://clang.llvm.org/docs/LanguageExtensions.html#deprecated)
• an empty string otherwise

Consider variants for deprecated attributes with and without comment string

• [[deprecated("TEXT")]] (C++14)
• __declspec(deprecated("TEXT")) (supported since Visual Studio 2005)
• __attribute__((deprecated("TEXT"))) (supported on gcc since which version?)