qmake does not support multiple windows .rc files in RC_FILE variable
i.e. If I write in .pro file:
RC_FILE = a.rc b.rc
just a.rc will be compiled.

This is a bug, I think.
Suppose, I have common rc file for icon (I have many application with the same icon and som other resource information), and specific rc file for current applciation.
Yes, I can use include directive in .rc file, but this is not suitable for me.

Variable should be called RC_FILES instead of RC_FILE. I do not know why the qmake developers decided to use just one file ....