[BitcodeReader] propagateAttributeTypes(): fix opaque pointer handling

Can't get the pointee type of an opaque pointer,
but in that case said attributes must already be typed,
so just don't try to rewrite them if they already are.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -3857,7 +3857,8 @@ void BitcodeReader::propagateAttributeTypes(CallBase *CB,
   for (unsigned i = 0; i != CB->arg_size(); ++i) {
     for (Attribute::AttrKind Kind : {Attribute::ByVal, Attribute::StructRet,
                                      Attribute::InAlloca}) {
-      if (!CB->paramHasAttr(i, Kind))
+      if (!CB->paramHasAttr(i, Kind) ||
+          CB->getParamAttr(i, Kind).getValueAsType())
         continue;
 
       CB->removeParamAttr(i, Kind);