Change an internal name in generated code to an exported name.
Generate codes for libffi ABI specifications.
Make the Libffi_abi module public.
Merge pull request #125 from yallop/abis

Generate codes for libffi ABI specifications.
Make CFLAGS available to subprocesses.

libffi-abigen needs access to CFLAGS to locate ffi.h
Save the result of CTYPES_FROM_PTR in CAMLlocalN-bound variables.

Pointers are heap-allocated nowadays.