From what it looks like, i386 cross-compiler can't find the appropriate libraries (it finds 64-bit ones, which are not compatible). I had this problem on Linux for quite some time and it seems to be solved by properly editing "fpc.cfg".
In my case, I had to edit these lines (there could be more):
# path to the gcclib
#ifdef cpui386
-Fl/usr/lib/gcc/x86_64-linux-gnu/4.9/32
#endif
#ifdef cpux86_64
-Fl/usr/lib/gcc/x86_64-linux-gnu/4.9
#endif
In the end of "fpc.cfg", I've added:
#IFDEF CPUI386
-Fl/usr/lib32
-Fl/usr/lib/i386-linux-gnu
#ENDIF
In case you find it useful, I've added my "fpc-prepare-x32.sh" script, which installs missing libraries (when building SVN trunk from scratch for i386 cross-compilation) and "fpc.cfg". In my config, I cross-compile from Linux x86_64 to Linux/i386, Linux/ARM-HF, Windows i386/x86_64, Android/ARMEL, Android/i386, Embedded/ARM and Embedded/AVR. However, I haven't tried seeding with 3.x though.