What steps should I take to compile Qt (version 4.8.x) for Visual Studio 2012?
I already carefully followed the instructions in the accepted answer of this question
Just creating a win32-msvc2012 directory with the changes below didn't work for me, there is more editing necessary. What exactly is necessary is described in the thread you already linked.
What I did, I went to win32-msvc2010.
There, open qmake.conf and change
QMAKE_COMPILER_DEFINES += _MSC_VER=1600 WIN32
to
QMAKE_COMPILER_DEFINES += _MSC_VER=1700 WIN32
Then I could configure using win32-msvc2010.
Also, I used these changes: http://qt-project.org/forums/viewthread/17771 (alzi's Version)