sha256.c and aes.c contain conflicting declarations, so we need to compile them
as separate units. This requires a bit more Makefile-shuffling; the build
directory now includes 'src' or 'lib' as appropriate, and we just mkdir -p
before each compilation.

think this got lost when mark added separate release/debug builds

Some of the crypto libs rely on UINT64_C, which in glibc 2.17 and earlier was
not defined for C++ code (see
https://sourceware.org/bugzilla/show_bug.cgi?id=15366).

Builds fuzzers using http://lcamtuf.coredump.cx/afl/

So that we can build everything together.

We want to stop aes_* and sha_* functions leaking out of our .so, as well as
internal _olm_* symbols.

This also means we need to link the unit tests against the objects. Possibly we
should distinguish between unit tests and integration tests.

Now that we have C and C++, we need to split the compile and link steps
(because we need different flags for the C and C++ files), so this is
easier with a Makefile.

Replace the python scripts for building the shared lib and tests with a
Makefile, which makes it easier to handle a mix of C and C++.

git-subtree-dir: lib/curve25519-donna
git-subtree-split: 28772f37a4b8a57ab9439b9e79b19f9abee686da