[MC] Remove addFragment. NFC

This was introduced in dcb71c0 to help
migrate away raw `operator new` and refactor the fragment
representation.

This is now unneeded after `MCStreamer::CurFrag` and
`MCSection::CurFragList` refactoring.

Author: MaskRay

llvm/include/llvm/MC/MCSection.h

@@ -198,18 +198,6 @@ class MCSection {
   iterator end() const { return {}; }
   bool empty() const { return !CurFragList->Head; }
 
-  void addFragment(MCFragment &F) {
-    // The formal layout order will be finalized in MCAssembler::layout.
-    if (CurFragList->Tail) {
-      CurFragList->Tail->Next = &F;
-      F.setLayoutOrder(CurFragList->Tail->getLayoutOrder() + 1);
-    } else {
-      CurFragList->Head = &F;
-      assert(F.getLayoutOrder() == 0);
-    }
-    CurFragList->Tail = &F;
-  }
-
   void dump() const;
 
   virtual void printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,

llvm/lib/MC/MCContext.cpp

@@ -201,7 +201,8 @@ MCDataFragment *MCContext::allocInitialFragment(MCSection &Sec) {
   assert(!Sec.curFragList()->Head);
   auto *F = allocFragment<MCDataFragment>();
   F->setParent(&Sec);
-  Sec.addFragment(*F);
+  Sec.curFragList()->Head = F;
+  Sec.curFragList()->Tail = F;
   return F;
 }
 

llvm/lib/MC/MCMachOStreamer.cpp

@@ -596,9 +596,7 @@ void MCMachOStreamer::createAddrSigSection() {
   MCSection *AddrSigSection =
       Asm.getContext().getObjectFileInfo()->getAddrSigSection();
   changeSection(AddrSigSection);
-  auto *Frag = getContext().allocFragment<MCDataFragment>();
-  Frag->setParent(AddrSigSection);
-  AddrSigSection->addFragment(*Frag);
+  auto *Frag = cast<MCDataFragment>(AddrSigSection->curFragList()->Head);
   // We will generate a series of pointer-sized symbol relocations at offset
   // 0x0. Set the section size to be large enough to contain a single pointer
   // (instead of emitting a zero-sized section) so these relocations are

llvm/lib/MC/MCWinCOFFStreamer.cpp

@@ -205,9 +205,7 @@ void MCWinCOFFStreamer::emitCOFFSafeSEH(MCSymbol const *Symbol) {
   changeSection(SXData);
   SXData->ensureMinAlignment(Align(4));
 
-  auto *F = getContext().allocFragment<MCSymbolIdFragment>(Symbol);
-  F->setParent(SXData);
-  SXData->addFragment(*F);
+  insert(getContext().allocFragment<MCSymbolIdFragment>(Symbol));
   getAssembler().registerSymbol(*Symbol);
   CSymbol->setIsSafeSEH();