Any workaround to make it work with single cpp file?
[/quote]
No, if you have only a single file AFAIK it has to be compiled in one run. You would need a special multi-threaded compiler. The best way to do so is having different modules which require only short compile runs each.
Jom basically starts several compiler instances in parallel. That brings the speed.
Moreover, you should really consider breaking up your code into several modules. The different makes are supporting to have partial compilation of the code by checking which files have been changed.
Without using jom you would have already a speedup of compilation.
[/quote]

I broke up the code into more CPP files. I found out that the most time consuming part is linking the boost library. So I couldn't get any improvement because it is only one class that uses the boost library (small code in my project but loads many boost's headers). I ended up using pre-compiled headers for boost and now the compile speed is good enough.

Any workaround to make it work with single cpp file?
[/quote]
No, if you have only a single file AFAIK it has to be compiled in one run. You would need a special multi-threaded compiler. The best way to do so is having different modules which require only short compile runs each.
Jom basically starts several compiler instances in parallel. That brings the speed.
Moreover, you should really consider breaking up your code into several modules. The different makes are supporting to have partial compilation of the code by checking which files have been changed.
Without using jom you would have already a speedup of compilation.

Any workaround to make it work with single cpp file?

I was hoping that breaking the code into more cpp files will not be necessary :(

It has only one cpp file, that is "main.cpp" with about 10000 lines. There are small project's header files and boost headers (.hpp) files. Qt lib DLLs are dynamically linked.