build: don't depend on the word size of nm output

the first column varies in length for different architectures

buildtools/scripts/abi_gen.sh

@@ -10,7 +10,7 @@ cat <<EOF
 set height 0
 set width 0
 EOF
-nm $SHAREDLIB | cut -c18- | egrep '^[DGTRVW]' | grep -v @ | cut -c3- | sort | while read s; do
+nm $SHAREDLIB | cut -d' ' -f2- | egrep '^[DGTRVW]' | grep -v @ | cut -c3- | sort | while read s; do
     echo "echo $s: "
     echo p $s
 done