1) I have added the GCC compilers from QtC for C and C++ targets, on options-> build&run->compilers tab (see gcc-avr-c.png, gcc-avr-c++.png):

GCC AVR (C) -> C:\Program Files (x86)\Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain\bin\avr-gcc.exe 

GCC AVR (C+) -> C:\Program Files (x86)\Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain\bin\avr-g++.exe

2) I have added a new Bare Metal Device

3) I have aded new non-qt AVR gcc Kit, based on AVR GCC compiler (see avr-kit.png)

4) I have created an simple C-like qbs project application, using the QtC wizard.

Attempt to opening for this application causes parsing errors like:

C:\Qt-meta\Tools\QtCreator\share\qtcreator\qbs\share\qbs\modules\cpp\GenericGCC.qbs:261: warning: The following properties are not set. Set them in your profile or product: cpp.architecture: you might want to re-run 'qbs-setup-toolchains'

 5) Next, I have added the 'avr' architecture to qbs profile settings of selected AVR kit (see avr-qbs-profile-settings.png, avr-qbs-profile-settings-view.png):

cpp.architecture avr
qbs.architecture avr

 6) Now, the project was successfully parsed and the application has been successfully compiled

avr.app.qbs:

import qbs

Project {
    minimumQbsVersion: "1.7.1"
    CppApplication {
        consoleApplication: true
        files: "main.c"
        Group {     // Properties for the produced executable
            fileTagsFilter: product.type
            qbs.install: true
        }
    }
}

main.c:

int main()
{
    return 0;
}

 7) This command:

avr-gcc -Wp,-dM -E -x c NUL > c:\Users\denis\Documents\avr-app\out.txt

gives output in 'avr-gcc-info.log'