g++: duplicate section has different size (only with -march=pentium4, mingw32)

[Frédéric Bron]

The attached minimal example (untar, make) shows the following warning
while linking:
A.o: duplicate section `.data$_ZN6ObjectIdE3barE[__ZN6ObjectIdE3barE]'
has different size
A.o: duplicate section
`.data$_ZGVN6ObjectIdE3barE[__ZGVN6ObjectIdE3barE]' has different size

I cross compile using g++ 4.6.4 or 4.7.3 from linux x86_64 to i686-pc-mingw32.
I observe that this happens only with -march=pentium4.
Also when I remove #include <iostream> that I do not use, the warning
disappears. I cannot figure out what this means and if it is important
or not. I wonder if it is because I did something wrong while building
the cross compiler...
However, I observe the same warning while using the cygwin cross
compiler i686-w64-mingw32 4.5.3 so I suspect it is not my cross
compiler.

Any help would be welcome.

Regards,

Frédéric
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