MCSymbolELF: Remove classof

The object file format specific derived classes are used in context
where the type is statically known. We don't use isa/dyn_cast and we
want to eliminate MCSymbol::Kind in the base class.

Author: MaskRay

llvm/include/llvm/MC/MCSymbol.h

@@ -281,8 +281,6 @@ class MCSymbol {
   /// Mark the symbol as undefined.
   void setUndefined() { Fragment = nullptr; }
 
-  bool isELF() const { return Kind == SymbolKindELF; }
-
   bool isCOFF() const { return Kind == SymbolKindCOFF; }
 
   bool isGOFF() const { return Kind == SymbolKindGOFF; }

llvm/include/llvm/MC/MCSymbolELF.h

@@ -48,8 +48,6 @@ class MCSymbolELF : public MCSymbol {
   void setMemtag(bool Tagged);
   bool isMemtag() const;
 
-  static bool classof(const MCSymbol *S) { return S->isELF(); }
-
 private:
   void setIsBindingSet() const;
 };

llvm/lib/Target/Mips/MipsAsmPrinter.cpp

@@ -1052,8 +1052,7 @@ void MipsAsmPrinter::EmitFPCallStub(
   //  __call_stub_fp_xxxx:
   //
   std::string x = "__call_stub_fp_" + std::string(Symbol);
-  MCSymbolELF *Stub =
-      cast<MCSymbolELF>(OutContext.getOrCreateSymbol(StringRef(x)));
+  MCSymbol *Stub = OutContext.getOrCreateSymbol(StringRef(x));
   TS.emitDirectiveEnt(*Stub);
   MCSymbol *MType =
       OutContext.getOrCreateSymbol("__call_stub_fp_" + Twine(Symbol));