Make type identifier escaping deterministic: hash() hashing lead to unpredictable random prefixes for long names across multiple Python runs.

Split a combined assert in two to avoid an unused C temp variable when assertions are disabled. (GH-3870)

Split a combined assert in two to avoid an unused C temp variable when assertions are disabled. (GH-3870)

`xml.etree.ElementTree.Element.getiterator()` was deprecated in Python
2.7 & 3.2 and removed in Python 3.9.

`xml.etree.ElementTree.Element.getiterator()` was deprecated in Python
2.7 & 3.2 and removed in the freshly released Python 3.9.

"synchapi.h" is not supposed to be included directly, and "windows.h" can break ... other stuff.
Let's see what we can do.

Looks like the usual macro on Windows is "_WIN32" and not "WIN32". Let's support both, to be on the safe side.

Move a memoryview test out of the "run" test directory since memoryview tests tend to be slow and have their own test directory.

- hash() hashing lead to unpredictable random prefixes for long names across multiple runs
- use a single regex run instead of repeated calls to replace()

Fixes https://github.com/cython/cython/issues/3843

Run both in the same job since the machines are quite fast with parallel processes, but setting one up is slow.

See, for example, https://isocpp.org/blog/2012/11/universal-references-in-c11-scott-meyers

Closes #3814

Show a more detailed error for unspecializable fused return types.