Use enum literal instead of constant

gen/dibuilder.cpp

@@ -290,7 +290,7 @@ llvm::DIType ldc::DIBuilder::CreateCompositeType(Type *type)
 
     // if we don't know the aggregate's size, we don't know enough about it
     // to provide debug info. probably a forward-declared struct?
-    if (sd->sizeok == 0)
+    if (sd->sizeok == SIZEOKnone)
 #if LDC_LLVM_VER >= 304
         return DBuilder.createUnspecifiedType(sd->toChars());
 #else

gen/module.cpp

@@ -536,7 +536,7 @@ void Module::genmoduleinfo()
             Logger::println("skipping interface '%s' in moduleinfo", cd->toPrettyChars());
             continue;
         }
-        else if (cd->sizeok != 1)
+        else if (cd->sizeok != SIZEOKdone)
         {
             Logger::println("skipping opaque class declaration '%s' in moduleinfo", cd->toPrettyChars());
             continue;

gen/structs.cpp

@@ -41,7 +41,7 @@ void DtoResolveStruct(StructDeclaration* sd)
     DtoType(sd->type);
 
     // if it's a forward declaration, all bets are off. The type should be enough
-    if (sd->sizeok != 1)
+    if (sd->sizeok != SIZEOKdone)
         return;
 
     // create the IrAggr

gen/typinf.cpp

@@ -596,7 +596,7 @@ void TypeInfoStructDeclaration::llvmDefine()
     StructDeclaration *sd = tc->sym;
 
     // can't emit typeinfo for forward declarations
-    if (sd->sizeok != 1)
+    if (sd->sizeok != SIZEOKdone)
     {
         sd->error("cannot emit TypeInfo for forward declaration");
         fatal();

ir/irtypestruct.cpp

@@ -88,7 +88,7 @@ IrTypeStruct* IrTypeStruct::get(StructDeclaration* sd)
     LOG_SCOPE;
 
     // if it's a forward declaration, all bets are off, stick with the opaque
-    if (sd->sizeok != 1)
+    if (sd->sizeok != SIZEOKdone)
         return t;
 
     // TODO:: Somehow merge this with IrAggr::createInitializerConstant, or