tests: Bump alignment for test structures to 64 bytes

Our core test structure is 36 bytes wide. Declaring it with a 32-bit
alignment should thus stripe it to 64 bytes. For some reason, clang+lld
lays them out with a 96-byte stride within the section (does it want an
entire 32-bit word when building with ASan?), getting the code wildly
confused when it tries to step through the structures.

So we could fix all our tests to avoid the fragile section dance, or we
could just waste another 4 bytes per test definition by bumping the
alignment up to 64 bytes, which seems to do enough to magically accord
with what clang+lld+ASan expect.

Signed-off-by: Daniel Stone <daniels@collabora.com>