Error building gcc-5.* with threads=win32

[niXman]

niXman 2015-08-02 14:37:
> niXman 2015-08-01 11:32:
>> Hi,
>> 
>> I have successfully built gcc-4.8.*/4.9.* as MinGW-w64 with
>> --enable-threads=win32 but I can't build gcc-5.* with the same
>> options.
>> Error occurs when building libatomic on stage 3.
>> 
>> If I change the '--enable-threads=win32' option on
>> '--enable-threads=posix' then it builds successfully.
>> 
>> 
>> configure: error: in
>> `/c/mingw520/i686-520-win32-sjlj-rt_v4-rev0/build/gcc-5.2.0/i686-w64-mingw32/64/libatomic':
>> configure: error: C compiler cannot create executables
>> See `config.log' for more details.
>> 
>> 
>> libatomic/config.log:
>> configure:3566: checking for C compiler default output file name
>> configure:3588:
>> /c/mingw520/i686-520-win32-sjlj-rt_v4-rev0/build/gcc-5.2.0/./gcc/xgcc
>> -B/c/mingw520/i686-520-win32-sjlj-rt_v4-rev0/build/gcc-5.2.0/./gcc/
>> -L/mingw32/i686-w64-mingw32/lib -L/mingw32/mingw/lib -isystem
>> /mingw32/i686-w64-mingw32/include -isystem /mingw32/mingw/include
>> -B/mingw32/i686-w64-mingw32/bin/ -B/mingw32/i686-w64-mingw32/lib/
>> -isystem /mingw32/i686-w64-mingw32/include -isystem
>> /mingw32/i686-w64-mingw32/sys-include  -m64 -g -O2 -pipe
>> -I/c/mingw520/i686-520-win32-sjlj-rt_v4-rev0/mingw32/opt/include
>> -I/c/mingw520/prerequisites/i686-zlib-static/include
>> -I/c/mingw520/prerequisites/i686-w64-mingw32-static/include
>> -fno-sync-libcalls  -march=i486 -mtune=i686 -fomit-frame-pointer
>> conftest.c  >&5
>> conftest.c:1:0: error: CPU you selected does not support x86-64 
>> instruction set
>> 
>> As you can see here are simultaneously used the '-m64 -march=i486
>> -mtune=i686' options.
>> 
>> 
>> Question is, why and how can I fix it?
> 
> This bug is also present in the gcc-trunk.

ping?