[llvm] [MC, X86] emitInstruction: remove virtual function calls due to Intel JCC Erratum (PR #96835)

[Fangrui Song via llvm-commits]

================
@@ -1546,3 +1547,32 @@ MCAsmBackend *llvm::createX86_64AsmBackend(const Target &T,
     return new ELFX86_X32AsmBackend(T, OSABI, STI);
   return new ELFX86_64AsmBackend(T, OSABI, STI);
 }
+
+namespace {
+class X86ELFStreamer : public MCELFStreamer {
+public:
+  X86ELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
----------------
MaskRay wrote:

I added `X86_MC::emitInstruction` to retain the support for COFF.

https://github.com/llvm/llvm-project/pull/96835