Fix dangling StubLinkerCPU::EmitDelegateInvoke in x86/Linux (#8444)

Several methods in StublicLinkerCPU (including EmitDelegateInvoke) are
available only when FEATURE_STUBS_AS_IL is defined.

This commit encloses their declaration with appropriate macro
(FEATURE_STUBS_AS_IL), and fix related build erros.

src/vm/comdelegate.cpp

@@ -2395,7 +2395,7 @@ PCODE COMDelegate::TheDelegateInvokeStub()
  }
  CONTRACT_END;
 
-#ifdef _TARGET_X86_
+#if defined(_TARGET_X86_) && !defined(FEATURE_STUBS_AS_IL)
  static PCODE s_pInvokeStub;
 
  if (s_pInvokeStub == NULL)
@@ -2415,7 +2415,7 @@ PCODE COMDelegate::TheDelegateInvokeStub()
  RETURN s_pInvokeStub;
 #else
  RETURN GetEEFuncEntryPoint(SinglecastDelegateInvokeStub);
-#endif // _TARGET_X86_
+#endif // _TARGET_X86_ && !FEATURE_STUBS_AS_IL
 }
 
 // Get the cpu stub for a delegate invoke.

src/vm/i386/cgencpu.h

@@ -43,6 +43,10 @@ EXTERN_C void STDCALL PInvokeStackImbalanceHelper(void);
 EXTERN_C void STDCALL CopyCtorCallStub(void);
 #endif // !FEATURE_CORECLR
 
+#ifdef FEATURE_STUBS_AS_IL
+EXTERN_C void SinglecastDelegateInvokeStub();
+#endif // FEATURE_STUBS_AS_IL
+
 BOOL Runtime_Test_For_SSE2();
 
 #ifdef CROSSGEN_COMPILE

src/vm/i386/stublinkerx86.h

@@ -377,13 +377,16 @@ class StubLinkerCPU : public StubLinker
  BOOL bShouldProfile);
 #endif // FEATURE_COMINTEROP && _TARGET_X86_
 
+#ifndef FEATURE_STUBS_AS_IL
  //===========================================================================
  // Computes hash code for MulticastDelegate.Invoke()
  static UINT_PTR HashMulticastInvoke(MetaSig* pSig);
 
+#ifdef _TARGET_X86_
  //===========================================================================
  // Emits code for Delegate.Invoke() any delegate type
  VOID EmitDelegateInvoke();
+#endif // _TARGET_X86_
 
  //===========================================================================
  // Emits code for MulticastDelegate.Invoke() - sig specific
@@ -392,6 +395,7 @@ class StubLinkerCPU : public StubLinker
  //===========================================================================
  // Emits code for Delegate.Invoke() on delegates that recorded creator assembly
  VOID EmitSecureDelegateInvoke(UINT_PTR hash);
+#endif // !FEATURE_STUBS_AS_IL
 
  //===========================================================================
  // Emits code to adjust for a static delegate target.
@@ -405,9 +409,11 @@ class StubLinkerCPU : public StubLinker
  //Worker function to emit throw helpers for array ops.
  VOID EmitArrayOpStubThrow(unsigned exConst, unsigned cbRetArg);
 
+#ifndef FEATURE_STUBS_AS_IL
  //===========================================================================
  // Emits code to break into debugger
  VOID EmitDebugBreak();
+#endif // !FEATURE_STUBS_AS_IL
 
 #if defined(_DEBUG) && (defined(_TARGET_AMD64_) || defined(_TARGET_X86_)) && !defined(FEATURE_PAL)
  //===========================================================================