Remove -cc1 -fconcepts-ts flag

The -fconcepts-ts flag has been deprecated for 5 releases now, so just
remove it, concepts is supported in C++20 mode.

clang/docs/ReleaseNotes.rst

@@ -485,6 +485,8 @@ Modified Compiler Flags
 
 Removed Compiler Flags
 -------------------------
+- Clang now no longer supports ``-cc1 -fconcepts-ts``.  This flag has been deprecated
+  and encouraged use of ``-std=c++20`` since Clang 10, so we're now removing it.
 
 New Pragmas in Clang
 --------------------

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -132,9 +132,6 @@ def err_fe_invalid_alignment : Error<
     "invalid value '%1' in '%0'; alignment must be a power of 2">;
 def err_fe_invalid_exception_model
    : Error<"invalid exception model '%select{none|sjlj|seh|dwarf|wasm}0' for target '%1'">;
-def warn_fe_concepts_ts_flag : Warning<
-  "-fconcepts-ts is deprecated - use '-std=c++20' for Concepts support">,
-  InGroup<Deprecated>;
 def err_fe_invalid_source_date_epoch : Error<
     "environment variable 'SOURCE_DATE_EPOCH' ('%0') must be a non-negative decimal integer <= %1">;
 

clang/include/clang/Driver/Options.td

@@ -5881,8 +5881,6 @@ def ftest_module_file_extension_EQ :
   Joined<["-"], "ftest-module-file-extension=">,
   HelpText<"introduce a module file extension for testing purposes. "
            "The argument is parsed as blockname:major:minor:hashed:user info">;
-def fconcepts_ts : Flag<["-"], "fconcepts-ts">,
-  HelpText<"Enable C++ Extensions for Concepts. (deprecated - use -std=c++2a)">;
 
 defm recovery_ast : BoolOption<"f", "recovery-ast",
   LangOpts<"RecoveryAST">, DefaultTrue,

clang/lib/Frontend/CompilerInvocation.cpp

@@ -491,9 +491,6 @@ static bool FixupInvocation(CompilerInvocation &Invocation,
   if (LangOpts.AppleKext && !LangOpts.CPlusPlus)
     Diags.Report(diag::warn_c_kext);
 
-  if (Args.hasArg(OPT_fconcepts_ts))
-    Diags.Report(diag::warn_fe_concepts_ts_flag);
-
   if (LangOpts.NewAlignOverride &&
       !llvm::isPowerOf2_32(LangOpts.NewAlignOverride)) {
     Arg *A = Args.getLastArg(OPT_fnew_alignment_EQ);