mmap returns void* and indicates failure via MAP_FAILED that is defined
to be ((void *)-1). Every mmap call has to be checked for failure and
thus posix.mman with mmap, but without MAP_FAILED is not very useful.

We cannot declare MAP_FAILED as enum, because enum assumes int. However
Cython documentation says

	4. If the header file uses macros to define constants, translate
	   them into a normal external variable declaration. ...

	(https://cython.readthedocs.io/en/latest/src/userguide/external_C_code.html#referencing-c-header-files)

So add proper declaration for MAP_FAILED to make posix.mman.mmap usable.

Move the setting of the new cythonize option "--no-docstrings" to a better place where it does not interfere with using `Cythonize` as a module.

* cythonize -D, --no-docstrings

Add `-D, --no-docstrings` option for the cythonize script.

* remove the short `-D` option, remaining only `--no-docstrings`

At module cleanup time, clear the module dict before the global references that its content might still be using.

Keep owned references to builtins module, "cython_runtime" module and preimport module to prevent crashes when they get removed from sys.modules. Generate cleanup code for them in the end.
Closes #2885.

Support CPython builds with docstrings disabled

Support CPython builds with docstrings disabled by wrapping docstring literals in the `PyDoc_STR()` macro.
Closes GH-884.

Closes GH-2884.

Disable "fast_gil" support in Py3<3.6 since Py3<3.5.2 lacks _PyThreadState_UncheckedGet() and crashes when calling PyThreadState_GET() without a thread state.

Issue a warning when casting a GIL-requiring function into a nogil function (which breaks GIL validation).
Closes GH-2879.

Fix reference in docs

See #2879.

Refactor parsing function in code coverage plugin to split the actual parsing code from the lookup code.

Exclude non-executable lines from coverage analysis (anything that does not generate a line trace call).

GH-1461: Include the signature line of cdef functions in the import-time line tracing and coverage report.

GH-1461: Include the signature line of cdef functions in the import-time line tracing and coverage report.

Allow condition in GILStatNode

Prevent the time stamps in the test runner from being captured together with the output of the C compiler.

Disable the new compiler warning about ambiguous exception return values when the function is external (and therefore possibly not under the control of the user).