traceroute: add VPATH to find libraries and avoid host contamination

Fixed:
make[1]: *** No rule to make target '-lm', needed by 'traceroute'.  Stop.

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>