Due to ASLR restrictions, preloading on Windows does not work with
any code that has preloading dependencies on internal classes.
This effectively makes it unusable for any non-trivial codebase.
Instead of pretending like preloading is going to work, only to
make people realize that it really doesn't once they get beyond
a dummy example, we disable support for preloading on Windows
entirely.
Closes GH-4999.
Also adds an --asan flag to run-tests.php to setup all the necessary
environment variables. Some tests are marked as skipped because they
are incompatible with asan or too slow.
I'm basing this on the DEBUG_ZTS build, which seems to give us the
most mileage.
Nikita Popov