fmemopen() is a function that is only provided with *NIX systems, so we
ought to check for its presence in order to build and run the tests
in fuzz/ fully, otherwise, we just skip the tests.
Also include headers according to how they are found, and add fallbacks
for Visual Studio that do not have stdint.h yet.
Large inputs on psl_registrable_domain() and psl_unregistrable_domain()
suffer from a O(N^2) behavior. This change limits N to avoid excessive
CPU usage.
At the same time we limit the fuzz corpora size to 64k which is far more
then we expect any real life domain to be.
Reported-by: OSS-Fuzz
Tim Rühsen
Chun-wei Fan