bpo-43244: Add pycore_compile.h header file

[vstinner]

Remove the compiler functions using "struct _mod" type, because the
public AST C API was removed:

• PyAST_Compile()
• PyAST_CompileEx()
• PyAST_CompileObject()
• PyFuture_FromAST()
• PyFuture_FromASTObject()

These functions were undocumented and excluded from the limited C API.

Rename functions:

• PyAST_CompileObject() => _PyAST_Compile()
• PyFuture_FromASTObject() => _PyFuture_FromAST()

Moreover, _PyFuture_FromAST() is no longer exported (replace
PyAPI_FUNC() with extern). _PyAST_Compile() remains exported for
test_peg_generator.

Remove also compatibility functions:

• PyAST_Compile()
• PyAST_CompileEx()
• PyFuture_FromAST()

https://bugs.python.org/issue43244

[vstinner]

I checked if the removed functions are used by the top PyPI 4000 projects: there is only typed_ast, the same one that I met in PR #24933.

vstinner@apu$ ./search.sh PyAST_Compile 2021-02-18/graphene-federation-0.1.0.tar.gz vstinner@apu$ ./search.sh PyAST_CompileEx 2021-02-18/graphene-federation-0.1.0.tar.gz vstinner@apu$ ./search.sh PyAST_CompileObject 2021-02-18/graphene-federation-0.1.0.tar.gz vstinner@apu$ ./search.sh PyFuture_FromASTObject 2021-02-18/graphene-federation-0.1.0.tar.gz vstinner@apu$ ./search.sh PyFuture_FromAST 2021-02-18/typed_ast-1.4.2.tar.gz 2021-02-18/graphene-federation-0.1.0.tar.gz 

graphene-federation-0.1.0.tar.gz contains a virtual environment which contains a Python binary (which contains the symbols). It can be safely ignored.