Does default Qt distribution for Windows use MinGW or MinGW-W64?

[Teh Me]

Hello. I just got a '__gthread_mutex_t' does not name a type error. I googled it and found out that it only appears on MinGW, but not on MinGW-W64. For some reason I was sure that Qt shipped MinGW-W64 by default. Looks like I was wrong. So here are my questions.
Why does Qt use MinGW instead of MinGW-W64?
Are there any Qt distributions with MinGW-W64, that are more 'official' than one mentioned here?

[Teh Me]

Ok, modern Qt does use mingw-w64. Thanks to malcom2073_ from irc for help. I'll look for error source in other place.