defs: only define ARRAYSIZE when needed
defs: only define ARRAYSIZE when needed

To make mingw cross compilation on Fedora 17 work.

In file included from src/common/autobuf.h:47:0,
                 from src/common/autobuf.c:42:
src/defs.h:103:0: error: "ARRAYSIZE" redefined [-Werror]
In file included from /usr/i686-w64-mingw32/sys-root/mingw/include/windef.h:137:0,
                 from /usr/i686-w64-mingw32/sys-root/mingw/include/windows.h:69,
                 from /usr/i686-w64-mingw32/sys-root/mingw/include/winsock2.h:23,
                 from ./src/win32/sys/time.h:47,
                 from src/defs.h:46,
                 from src/common/autobuf.h:47,
                 from src/common/autobuf.c:42:
/usr/i686-w64-mingw32/sys-root/mingw/include/winnt.h:483:0: note: this is the location of the previous definition

Signed-off-by: Ferry Huberts <66e11f9f5d965b69497c7e73d5e808f8b13c1218@pelagic.nl>

cholin/olsrd,zioproto/olsrd,ninuxorg/olsrd,diogomg/olsrd-binary-heap,sebkur/olsrd,nolith/olsrd,servalproject/olsr,cholin/olsrd,acinonyx/olsrd,acinonyx/olsrd,ninuxorg/olsrd,diogomg/olsrd-binary-heap,diogomg/olsrd,acinonyx/olsrd,diogomg/olsrd,tdz/olsrd,duydb2/olsr,cholin/olsrd,sebkur/olsrd,duydb2/olsr,diogomg/olsrd,duydb2/olsr,zioproto/olsrd,duydb2/olsr,sebkur/olsrd,diogomg/olsrd-binary-heap,diogomg/olsrd,duydb2/olsr,tdz/olsrd,zioproto/olsrd,acinonyx/olsrd,diogomg/olsrd,ninuxorg/olsrd,cholin/olsrd,cholin/olsrd,tdz/olsrd,diogomg/olsrd-binary-heap,tdz/olsrd,duydb2/olsr,sebkur/olsrd,duydb2/olsr,zioproto/olsrd,sebkur/olsrd,nolith/olsrd,acinonyx/olsrd,servalproject/olsr,nolith/olsrd,diogomg/olsrd,ninuxorg/olsrd,diogomg/olsrd-binary-heap,diogomg/olsrd-binary-heap,nolith/olsrd,sebkur/olsrd,servalproject/olsr,ninuxorg/olsrd,duydb2/olsr,diogomg/olsrd-binary-heap,tdz/olsrd,diogomg/olsrd,servalproject/olsr,servalproject/olsr,servalproject/olsr,nolith/olsrd,zioproto/olsrd