Embarcadero has RTM'd RAD Studio, Delphi and C++Builder 10.3 Rio (version 20.0) today. You can read the press release here. Included in the release are several C++ compilers.
Note: BCC32C and BCC32X Clang-enhanced compilers are based on Clang/LLVM 5.0.2 which supports C++17.
Clang 5 and later implement all the features of the ISO C++ 2017 standard.
C++ Support in Clang - https://clang.llvm.org/cxx_status.html
C++17 implementation status - https://clang.llvm.org/cxx_status.html#cxx17
Note: the other Clang enhanced compilers are based on Clang / LLVM 3.3 and support the feature complete ISO C++ 11 standard - http://releases.llvm.org/3.3/tools/clang/docs/ReleaseNotes.html
If you are wondering about C++ compilers for Android 64 bit, Linux and other platforms, you should read the recent RAD Studio Roadmap article published in August 2018.