[UserManual] Update the C++ standard support

[Mordante]

Summary

This brings the state in sync with http://clang.llvm.org/cxx_status.html.

[merge_guards_bot]

Unit tests: pass. 61168 tests passed, 0 failed and 728 were skipped.

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[Mordante]

Friendly ping, it would be nice to get this in the next release.

[xbolva00]

+1

clang/docs/UsersManual.rst

2557

Clang ? :)

[Mordante]

clang/docs/UsersManual.rst

2557

I wondered about this before but we use both clang and Clang in the manual. So for now I decided not to make that change. If wanted I can make a separate patch doing the renaming. Should we then also change clang-cl to Clang-cl?

clang/docs/UsersManual.rst

 example, ``-fms-compatibility-version=19`` will enable C++14 features and define
 ``char16_t`` and ``char32_t`` as builtin types.
 
 .. _cxx:
 
 C++ Language Features
 =====================
 
 clang fully implements all of standard C++98 except for exported
-templates (which were removed in C++11), and all of standard C++11
-and the current draft standard for C++1y.
+templates (which were removed in C++11), and all of standards C++11, C++14,
+and C++17. It has experimental support for the current draft standard C++2a.
 
 Controlling implementation limits
 ---------------------------------
 
 .. option:: -fbracket-depth=N
 
   Sets the limit for nested parentheses, brackets, and braces to N.  The
   default is 256.