Detect modified files during qmake

[onurA]

How does qt detect if the build is necessary or not, e.g. if a source file or in my case a resource file (.qrc) was modified after the last build? Is there a flag for each file?
What I exactly want to do is, to send a system command for resource compilation by adding this to the .pro file:
system(rcc -binary -no-compress resource.qrc -o resource.rcc)
And I want to do it only if the resource.qrc file modified after the last qmake. Is that possible and how?

Final version should be: if(resource_modified) {COMPILE RESOURCE}

[jsulm]

For source files (c/c++) it is not the job for qmake - this is done by make.
For built in resource files it is probably the same - make detects whether the resource file was changed or not.

[onurA]

@jsulm
I need it for the rcc command. Whenever I run rcc in terminal, the binary output is re-generated, although the .qrc is the same.

Is there a way to check it in qmake for example? Like a flag?
Thanks in advance!