CPP-5803 S7035 Add exception for casts to bool

rules/S7035/cfamily/rule.adoc

@@ -65,7 +65,20 @@ This rule raises an issue when an enum is converted to an integral value without
 
 === Exceptions
 
-Unscoped enums with no underlying type specified have an implementation-defined implicit underlying type. Calling `std::to_underlying` on them wouldn't make the code more portable so this rule doesn't raise on them.
+The result of casting any integer type to `bool` does not depend on the specific integer type.
+For the same reason, casting an enumeration to `bool` does not depend on the underlying type of enumerator, so this rule does not raise.
+
+[source,cpp]
+----
+enum class Enum {A, B, C};
+void foo(Enum e) {
+  auto i = static_cast<bool>(e); // Compliant by exception, the intent is obvious
+  ...
+}
+----
+
+Unscoped enums with no underlying type specified have an implementation-defined implicit underlying type. 
+Calling `std::to_underlying` on them would not make the code more portable so this rule does not raise on them.
 
 [source,cpp]
 ----