Allow to compile legacy lexx software

Summary:
Bison flex and libfl will allow to process .l files
and convert them in C code, then build them.

To clone repositories, ca-certificates could be useful too.

The use of build-essential ensures we've the C headers,
that avoids to have a compiler but no stdio.h available.

Test Plan: Build valspeak

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2480