add libiberty-dev to tools/get-deps.pl

fix link issue on Ubuntu 14.04

```bash
gcc -g -I. -I../../ -I../../libctf -I../../common -I../../uts/common -I../../linux -I/usr/include/libdwarf -o ../../build/ctfconvert ../../build/ctfconvert.obj/ctfconvert.o ../../build/ctfconvert.obj/alist.o ../../build/ctfconvert.obj/ctf.o ../../build/ctfconvert.obj/dwarf.o ../../build/ctfconvert.obj/hash.o ../../build/ctfconvert.obj/iidesc.o ../../build/ctfconvert.obj/input.o ../../build/ctfconvert.obj/list.o ../../build/ctfconvert.obj/memory.o ../../build/ctfconvert.obj/merge.o ../../build/ctfconvert.obj/output.o ../../build/ctfconvert.obj/st_bugs.o ../../build/ctfconvert.obj/st_parse.o ../../build/ctfconvert.obj/stabs.o ../../build/ctfconvert.obj/stack.o ../../build/ctfconvert.obj/strtab.o ../../build/ctfconvert.obj/symbol.o ../../build/ctfconvert.obj/tdata.o ../../build/ctfconvert.obj/traverse.o ../../build/ctfconvert.obj/util.o ../../build/libctf.a -ldwarf -liberty -lelf -lz
/usr/bin/ld: cannot find -liberty
collect2: error: ld returned 1 exit status
make[3]: *** [../../build/ctfconvert] Error 1
make[2]: *** [all] Error 2
make[1]: *** [do_cmds] Error 2
tools/bug.sh
make: *** [all] Error 1
```