Fix shared/static settings when building vs. NaCl library

Make sure the shared lib build is really disabled when compiling vs.
NaCl:

moved settings before libtool initialization
fixed parameter name
Fix NaCl builds for *BSD

From what I see there is a difference between *BSD and Linux when
linking vs. toxcore which has been bulit vs. the NaCl library:

on Linux it only links if NaCl's object files (i.e. randombytes.o) is
present in the linker options, however on *BSD systems this will cause a
linking error, see:
https://github.com/Tox/toxic/issues/31#issuecomment-38224441

This commit makes sure that we do not add the NaCl object files to our
pkg-config settings on *BSD, but do add them on Linux.
Merge pull request #815 from jin-eld/nacl-fix-3

More NaCl related fixes