Add the ability to show preprocessed and ASM output for a given C/C++ file

It would be nice to have an integrated ability to have QBS produce a preprocessed source file or ASM file, that is accessible from IDEs. For example, Xcode has such a feature: Product > Perform Action > Preprocess

This should be doable by adding an option to the compiler command line that would otherwise be run, for the given source file.

GCC also has -save-temps which'll compile to an object file, preprocessed output, and ASM in a single pass. MSVC requires separate invocations, I think.

Given that we now have (or almost have?) a build single file option, I think these options would also be valuable for debugging.