libpcap: sparc needs -fPIC as sparc64/microblaze

Fixes nmap build for sparc.

Fixes:
 http://autobuild.buildroot.net/results/8e476939f1daaa20c316dbd0508fa343034f2397



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