Also tried the official mingw package. The debugger has the I: bug, but the compiler doesn't have redundant-decl warning. First I tried to copy-paste the debugger from mingw-w64 to mingw, but it seems the w64 version is very different and it's asking for a python .dll which is missing when you move the .exe. So w64 dudes are using python in programming gcc and gdb. That's wrong in so many ways, but then I realized I can point the compiler to mingw official and debugger to w64 version.
I never realized that Windows version of gcc was in such a low state. These people don't seem to know what they are doing.