Get libgcrypt tests passing.

I patched the sources to accept an "insecure" source of entropy
which in emscripten is the browser's Math.random.

The t-kdf tests requires more than 16 MiB of memory. At this time
the -s TOTAL_MEMORY=X option doesn't actually work with
EMMAKEN_JUST_CONFIGURE=true EMCONFIGURE_JS=true but I hope it will
soon. Otherwise I'll come up another patch.