live555: fix shared library build on x86

-fPIC is required for shared libraries on x86.

Fixes:
http://autobuild.buildroot.net/results/6e7/6e78d3e29856c25d233f1629c31bc15f7ecb2f89/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>