C++ front-end: bool is also an integral type

Visual Studio uses enums with a bool subtype in header files.

Author: tautschnig

buildspec-windows.yml

@@ -47,7 +47,6 @@ phases:
         Remove-Item cbmc\byte_update5 -Force -Recurse
         Remove-Item cbmc\byte_update6 -Force -Recurse
         Remove-Item cbmc\byte_update7 -Force -Recurse
-        Remove-Item cpp\virtual1 -Force -Recurse
         Remove-Item goto-gcc -Force -Recurse
         cd ..
         cd jbmc/regression

src/cpp/cpp_typecheck_enum_type.cpp

@@ -155,11 +155,10 @@ void cpp_typecheckt::typecheck_enum_type(typet &type)
     else
     {
       typecheck_type(type.subtype());
-      if(type.subtype().id()==ID_signedbv ||
-         type.subtype().id()==ID_unsignedbv)
-      {
-      }
-      else
+      if(
+        type.subtype().id() != ID_signedbv &&
+        type.subtype().id() != ID_unsignedbv &&
+        type.subtype().id() != ID_c_bool)
       {
         error().source_location=type.source_location();
         error() << "underlying type must be integral" << eom;