Instead of using Cython's old_style_globals option, we use the new user_globals from #12446 to access globals().

In order to support

sage: sage_eval( ("f(x)=x^2", "f(1)") )

we make a small change to the preparser: we ensure that f(x) = ... makes x available both as global and as local.

Depends on #12446
Depends on #18084

Component: cython

Author: Jeroen Demeyer

Branch/Commit: u/jdemeyer/stop_using_old_style_globals @ 9ccd889

Issue created by migration from https://trac.sagemath.org/ticket/18083