Sounds like your x86/Makefile is not getting generated.
Can you open a regular command window and prep the shell using the bbndk-env.bat file from your BBNDK installation dir, then type the following from the top level of your demo project? (Replace YOURPROJECT.pro with whatever your .pro file actually is)
qmake -spec unsupported/blackberry-x86-qcc -o x86/Makefile YOURPROJECT.pro CONFIG+="simulator debug_and_release"
Does the x86/Makefile get generated? Any errors?
Can you post the Makefile for the demo you are using?