Fix libxbmc linux (closes #14914)

This is an attempt at fixing libxbmc.so on _linux_
Its been broken since 7ef9badfde72fac8ad693c45946a00f2dd29c4b4

According to reports on http://forum.xbmc.org/showthread.php?tid=132919&page=48 this patch works 
I'm unsure if -BSymbolic has any side effects, although several distros (e.g. ubuntu) use this per default.
@t-nelson ping