Fix link to Tier 2 mingw-builds version

We switched to rev3 in the binary packages to get in a gdb fix.

This change does not apply to Qt 5.

Change-Id: I0328c35671e84e3b592c99cf5ebe8d1cce1ea80f
Reviewed-by: Akseli Salovaara <akseli.salovaara@digia.com>
Doc: Mention that MINGWM10.DLL only applies to MinGW 4.4

Mingw-builds based 4.8.2 has different files ...

Change-Id: I99659c4f6e46673c6077a890b744e355c5226d36
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>