[Clang] Stop demoting ElementCount/TypeSize conversion errors to warnings.

[paulwalker-arm]

This option was our pragmatic way to ensure scalable vector based toolchains remained useful whilst the kinks were worked out. We've a few releases under our belts now and I feel that enough works to consider further errors as something we should not be hiding.

[reames]

This makes perfect sense to me. LGTM

[sdesmalen]

It gives me great joy to see this code removed :)

clang/lib/Driver/ToolChains/Clang.cpp

#endif
   std::string CPU = getCPUName(D, Args, Triple, /*FromAs*/ false);
   if (!CPU.empty()) {
     CmdArgs.push_back("-target-cpu");
     CmdArgs.push_back(Args.MakeArgString(CPU));
   }
 
   RenderTargetOptions(Triple, Args, KernelOrKext, CmdArgs);
 
-  // FIXME: For now we want to demote any errors to warnings, when they have
-  // been raised for asking the wrong question of scalable vectors, such as
-  // asking for the fixed number of elements. This may happen because code that
-  // is not yet ported to work for scalable vectors uses the wrong interfaces,
-  // whereas the behaviour is actually correct. Emitting a warning helps bring
-  // up scalable vector support in an incremental way. When scalable vector
-  // support is stable enough, all uses of wrong interfaces should be considered
-  // as errors, but until then, we can live with a warning being emitted by the
-  // compiler. This way, Clang can be used to compile code with scalable vectors
-  // and identify possible issues.
-  if (isa<AssembleJobAction>(JA) || isa<CompileJobAction>(JA) ||
-      isa<BackendJobAction>(JA)) {
-    CmdArgs.push_back("-mllvm");
-    CmdArgs.push_back("-treat-scalable-fixed-error-as-warning");
-  }
-
   // These two are potentially updated by AddClangCLArgs.
   codegenoptions::DebugInfoKind DebugInfoKind = codegenoptions::NoDebugInfo;
   bool EmitCodeView = false;
 
   // Add clang-cl arguments.
   types::ID InputType = Input.getType();
   if (D.IsCLMode())
     AddClangCLArgs(Args, InputType, CmdArgs, &DebugInfoKind, &EmitCodeView);