Reland "Add macro to suppress -Wunnecessary-virtual-specifier" (#141091)

This fixes #139614 on non-clang compilers by moving `__has_warning`
completely inside the `#if defined(__clang__)` block. This prevents a
parse failure from compilers which don't recognize `__has_warning`.

Original description:
Followup to #138741.

This adds the requested macro to silence
`-Wunnecessary-virtual-specifier` when declaring virtual anchor
functions in `final` classes, per [LLVM
policy](https://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers).

It also cleans up any remaining instances of the warning, allowing us to
stop disabling it when we build LLVM.

10 files changed, 15 insertions, 15 deletions

diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 9290ff3..69ad18f4 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -173,7 +173,7 @@ class PragmaCommentDecl final
                     PragmaMSCommentKind CommentKind)
       : Decl(PragmaComment, TU, CommentLoc), CommentKind(CommentKind) {}
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   static PragmaCommentDecl *Create(const ASTContext &C, TranslationUnitDecl *DC,
@@ -207,7 +207,7 @@ class PragmaDetectMismatchDecl final
                            size_t ValueStart)
       : Decl(PragmaDetectMismatch, TU, Loc), ValueStart(ValueStart) {}
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   static PragmaDetectMismatchDecl *Create(const ASTContext &C,
@@ -5024,7 +5024,7 @@ public:
 ///   export void foo();
 /// \endcode
 class ExportDecl final : public Decl, public DeclContext {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 private:
   friend class ASTDeclReader;
diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index d40d11c..df76e6f 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -3297,7 +3297,7 @@ class LifetimeExtendedTemporaryDecl final
 
   mutable APValue *Value = nullptr;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   LifetimeExtendedTemporaryDecl(Expr *Temp, ValueDecl *EDecl, unsigned Mangling)
       : Decl(Decl::LifetimeExtendedTemporary, EDecl->getDeclContext(),
diff --git a/clang/include/clang/AST/DeclFriend.h b/clang/include/clang/AST/DeclFriend.h
index 1644e2d..1f8c210 100644
--- a/clang/include/clang/AST/DeclFriend.h
+++ b/clang/include/clang/AST/DeclFriend.h
@@ -52,7 +52,7 @@ class ASTContext;
 class FriendDecl final
     : public Decl,
       private llvm::TrailingObjects<FriendDecl, TemplateParameterList *> {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   using FriendUnion = llvm::PointerUnion<NamedDecl *, TypeSourceInfo *>;
diff --git a/clang/include/clang/AST/DeclOpenMP.h b/clang/include/clang/AST/DeclOpenMP.h
index cf38388..2d07f9d 100644
--- a/clang/include/clang/AST/DeclOpenMP.h
+++ b/clang/include/clang/AST/DeclOpenMP.h
@@ -110,7 +110,7 @@ public:
 class OMPThreadPrivateDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPThreadPrivateDecl(DeclContext *DC = nullptr,
                        SourceLocation L = SourceLocation())
@@ -418,7 +418,7 @@ class OMPRequiresDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
   friend class ASTDeclReader;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPRequiresDecl(DeclContext *DC, SourceLocation L)
       : OMPDeclarativeDirective<Decl>(OMPRequires, DC, L) {}
@@ -475,7 +475,7 @@ class OMPAllocateDecl final : public OMPDeclarativeDirective<Decl> {
   friend class OMPDeclarativeDirective<Decl>;
   friend class ASTDeclReader;
 
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   OMPAllocateDecl(DeclContext *DC, SourceLocation L)
       : OMPDeclarativeDirective<Decl>(OMPAllocate, DC, L) {}
diff --git a/clang/include/clang/Driver/Action.h b/clang/include/clang/Driver/Action.h
index 92bb193..7aecfd8 100644
--- a/clang/include/clang/Driver/Action.h
+++ b/clang/include/clang/Driver/Action.h
@@ -267,7 +267,7 @@ public:
 /// programming model implementation needs and propagates the offloading kind to
 /// its dependences.
 class OffloadAction final : public Action {
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
 public:
   /// Type used to communicate device actions. It associates bound architecture,
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 6680a45..b423e2a 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -895,7 +895,7 @@ public:
   /// with a vtable when the vtable is emitted. Sema is final and not
   /// polymorphic, but the debug info size savings are so significant that it is
   /// worth adding a vtable just to take advantage of this optimization.
-  virtual void anchor();
+  LLVM_DECLARE_VIRTUAL_ANCHOR_FUNCTION();
 
   const LangOptions &getLangOpts() const { return LangOpts; }
   OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
diff --git a/clang/lib/AST/ByteCode/InterpFrame.h b/clang/lib/AST/ByteCode/InterpFrame.h
index 360e6bf..cfebe93 100644
--- a/clang/lib/AST/ByteCode/InterpFrame.h
+++ b/clang/lib/AST/ByteCode/InterpFrame.h
@@ -119,7 +119,7 @@ public:
   CodePtr getRetPC() const { return RetPC; }
 
   /// Map a location to a source.
-  virtual SourceInfo getSource(CodePtr PC) const;
+  SourceInfo getSource(CodePtr PC) const;
   const Expr *getExpr(CodePtr PC) const;
   SourceLocation getLocation(CodePtr PC) const;
   SourceRange getRange(CodePtr PC) const;
diff --git a/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp b/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
index f746b48..9e27e63 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
@@ -323,7 +323,7 @@ public:
   CheckVarsEscapingDeclContext(CodeGenFunction &CGF,
                                ArrayRef<const ValueDecl *> TeamsReductions)
       : CGF(CGF), EscapedDecls(llvm::from_range, TeamsReductions) {}
-  virtual ~CheckVarsEscapingDeclContext() = default;
+  ~CheckVarsEscapingDeclContext() = default;
   void VisitDeclStmt(const DeclStmt *S) {
     if (!S)
       return;
diff --git a/clang/lib/CodeGen/CGStmtOpenMP.cpp b/clang/lib/CodeGen/CGStmtOpenMP.cpp
index 803c7ed..89a79a7 100644
--- a/clang/lib/CodeGen/CGStmtOpenMP.cpp
+++ b/clang/lib/CodeGen/CGStmtOpenMP.cpp
@@ -4783,7 +4783,7 @@ class CheckVarsEscapingUntiedTaskDeclContext final
 
 public:
   explicit CheckVarsEscapingUntiedTaskDeclContext() = default;
-  virtual ~CheckVarsEscapingUntiedTaskDeclContext() = default;
+  ~CheckVarsEscapingUntiedTaskDeclContext() = default;
   void VisitDeclStmt(const DeclStmt *S) {
     if (!S)
       return;
diff --git a/clang/lib/Driver/ToolChains/Hexagon.h b/clang/lib/Driver/ToolChains/Hexagon.h
index e35a224..033d9b4 100644
--- a/clang/lib/Driver/ToolChains/Hexagon.h
+++ b/clang/lib/Driver/ToolChains/Hexagon.h
@@ -42,8 +42,8 @@ public:
   bool hasIntegratedCPP() const override { return false; }
   bool isLinkJob() const override { return true; }
 
-  virtual void RenderExtraToolArgs(const JobAction &JA,
-                                   llvm::opt::ArgStringList &CmdArgs) const;
+  void RenderExtraToolArgs(const JobAction &JA,
+                           llvm::opt::ArgStringList &CmdArgs) const;
   void ConstructJob(Compilation &C, const JobAction &JA,
                     const InputInfo &Output, const InputInfoList &Inputs,
                     const llvm::opt::ArgList &TCArgs,