libpcap: fix sparc64 build, -fPIC required

Should fix following autobuilder issues:
http://autobuild.buildroot.net/results/e79353496aa91848c76f15c561efdd84476c20ac/
http://autobuild.buildroot.net/results/a859ecb153838837e9a73b47ed7e1105d6be55ac/
http://autobuild.buildroot.net/results/f2ce1899a1144bec23fb25f4ce36dc78d768f8a8/



[Thomas: s/needs/need/ as suggested by Baruch.]

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>