gcc: fix libstdc++_pic for AVR32

It is not clear why 300-libstdc++-pic.patch pre-applied to
gcc-4.2.2-avr32-2.1.5 seems to have come from some older version
of gcc (as early as 4.0.3). This older patch incorrectly refers to
object files to be included in the library libstdc++_pic.a as *.o,
while their location seems to be in .libs/*.o (see the contents at
e.g. https://github.com/ZigFisher/Midge/blob/master/toolchain/gcc/4.0.3/300-libstdc%2B%2B-pic.patch ).
The same patch for gcc 4.1.0 refers to the files as .libs/*.o (see
https://github.com/ZigFisher/Midge/blob/master/toolchain/gcc/4.1.0/300-libstdc%2B%2B-pic.patch

 ).
This patch corrects rules in Makefile.in.

Signed-off-by: Alexander Lukichev <alexander.lukichev@gmail.com>
Acked-by: Simon Dawson <spdawson@gmail.com>
Tested-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>