source files referenced from qrc files might get compiled

If you have files with implicit make rules listed in a qrc file, make is trying to compile those files with a compiler.
This example has 2 resource files, "resource" and "resouce.c".
If "resource.c" is newer than "resource" make is trying to compile it, which will not succeed because it does not contain valid C code.

Step to reproduce:

1. Download three attachments
2. Create 2 empty files ("resource.c" has to have newer date)

touch resource
touch resource.c

3. qmake && make

[snip]
gcc [snip] resource.c -o resource
[error message]

As real life use case see "qtbase/tests/auto/corelib/io/qdir/android_testdata.qrc" triggering this issue.