[Cython] Broken C++ compile test

[Stefan Behnel]

Hi,

the question by Czarek Tomczak on the users list made me stumble into this
old C++ test:

https://github.com/cython/cython/blob/master/tests/compile/cpp_operators.pyx

It's completely broken and only failed to fail because it was never
executed. Apparently, the test runner shadowed it with the test of the same
name in the tests/run/ directory.

Stefan