atomic link failures for ArcticFox

Hi,

trying this PR on NetbSD... I don't like all details, but I couldn't do 
it better, so I wanted to test it.
https://github.com/rmottola/Arctic-Fox/pull/101

stub symbols now appear fine, but I end up with:

584:20.85 ld: ../../toolkit/library/libxul.so: undefined reference to 
`__atomic_fetch_add_8'
584:20.85 ld: ../../toolkit/library/libxul.so: undefined reference to 
`__atomic_store_8'
584:20.85 ld: ../../toolkit/library/libxul.so: undefined reference to 
`__atomic_load_8'
584:20.86 ld: ../../toolkit/library/libxul.so: undefined reference to 
`__atomic_fetch_sub_8'


do I need -latomic like on linux PPC?

It appears not to exist.. do I need to install it?

Riccardo