Fix for the -fvisibility=hidden problem.

'man ld' revealed the secret. Flag -keep_private_externs seems to
do what we want.
Keeping upto date with Tristan's vesrion

Merge branch 'master' of https://github.com/travitch/whole-program-llvm
Deadcode and dead notes removal.
Merge pull request #14 from SRI-CSL/master

Small fix for Darwin