Closes GH-3031

* REF: make Utils dependency-free by moving search_include_directories to Main
* BUG: prefer sys.path before Cython/Include when searching for pxd files

CPython bpo-37221 reverts that backwards incompatible
change to the PyCode_New API, replacing it with a new
PyCode_NewWithPosOnlyArgs function.

The regex to match the gdb version is not intended to be interpreted as a regular string, it is designed to be used as-is as a regex.  This lets python know that minor detail.

And make it more flexible in terms of API change.

Current checks breaks when setting 0.10.0 as a Pythran version :-/

Closes GH-2976.

This was broken by the attempt to exclude C++ operations from true division.

Move the variable declarations in a C helper function to where they are actually used to avoid "unused" warnings in Py3.

This fixes Github issue #1950.

Fix compile error with 3.8

Closes GH-2936.

Closes GH-2939.

GH-2919: Prevent tuple constants that compare equal but have different item types from being merged into one.