I use the prefix because I have had the auto detect change the path without any warning!
Using the prefix I at least get an error with the bit type has switch!
If by "I use the prefix" means that you changed the C::B code then I find this to be not the best solution to the above problem:
1. Only MinGW uses "mingw32-" prefix and AFAICT, this distribution has been on its way out and has been superseded by mingw-64.
2. Changing the "base" GCC compiler settings affects (read "breaks") the custom compiler configurations derived from it.
But again, I know little about C::B so I am probably missing something here.