I found many posts about this topic but did not saw any practical solution, but maybe I did not read the right articles. So my recent experiments brought the following insight:
Tools compiled with Mingw do not like spaces in the path name
The experiments in cmd.exe fixed the problem reproducable, if there was no spaces in the PATH. Unfortunately, both, the english Windows and AS6 push spaces in the path name.
@rem using path with spaces: FAIL @rem set PATH="C:\Program Files\Atmel\Atmel Studio 6.0\extensions\Atmel\AVRGCC\184.108.40.206\AVRToolchain\bin" @rem using path without spaces: PASS set PATH=C:\ProgramXFiles\Atmel\AtmelXStudioX6.0\extensions\Atmel\AVRGCC\220.127.116.11\AVRToolchain\bin make -C src any900 MKDIR=gmkdir