SEGV in ristretto_gen_tables on Travis CI (Linux/clang)

[tarcieri]

The ristretto_gen_tables executable, which is used to generate ristretto_tables.c, sporadically segfaults on Travis CI when compiled with Linux/clang:

https://travis-ci.org/Ristretto/libristretto255/jobs/416021686#L471

This means our memory safety problems aren't just limited to bindgen-generated code (#22). We appear to have problems with pure C code as well.

Curiosities:

• The OS X build with clang always seems to succeed
• So far this has always impacted PR builds and never builds on master

[tarcieri]

I enabled ASAN in this PR: #26

That seems to have "fixed" the problem. I'll leave this issue open as it probably warrants more investigation.

I've been unable to reproduce it locally.

[tarcieri]

Attempted to run ristretto_gen_tables under lldb in #34. Like with ASAN, this prevents the problem from happening (i.e. heisenbug).