[flang] Correct TypeCode::IsLogical()

F18 is using the type codes for C's "least" int types to encode
the various kinds of Fortran's LOGICAL intrinsic type; update
the IsLogical() predicate accordingly.  (This member function
isn't yet used anywhere, so this patch is nearly an NFC.)

Differential Revision: https://reviews.llvm.org/D100323

flang/runtime/type-code.h

@@ -45,7 +45,7 @@ class TypeCode {
   }
   constexpr bool IsLogical() const {
     return raw_ == CFI_type_Bool ||
-        (raw_ >= CFI_type_int_fast8_t && raw_ <= CFI_type_int_fast64_t);
+        (raw_ >= CFI_type_int_least8_t && raw_ <= CFI_type_int_least64_t);
   }
   constexpr bool IsDerived() const { return raw_ == CFI_type_struct; }
   constexpr bool IsIntrinsic() const { return IsValid() && !IsDerived(); }