gfp_array non-thread-safe

[sandmanhome]

There are global variables in Galois.c, and lazy initialization in multiple functions.

https://github.com/tsuraan/Jerasure/blob/414c96ef2b9934953b6facb31d803d79b1dd1405/src/galois.c#L173

The above problems make multithreaded coding crash.