It says you're missing lrelease.exe in
C:\Qt\4.8.6\bin
It's location is specified in the .pro file
win32:QMAKE_LRELEASE = $$[QT_INSTALL_BINS]\\lrelease.exe
If it's altogether missing, try reinstalling QT.
Hmmm I'll try that next time I give it a go as I've uninstalled everything ATM as it was causing me angst, I even tried to use the automatic EasyWinBuilder for the standard Bitcoin client & it errors on a newer build of QT & exits because it can't install it maybe because zip was corrupt but I have tried it on numerous occasions with the same result.
I might try a different version of QT to see if that gets it working when messing around with it again.
I think it might just be easier to setup a Linux VM & then install dependencies, etc & compile a Windows Qt that way, but this will be my first time using Linux....