gh-157695: Rename HAVE_ACOSPI to _Py_HAVE_ACOSPI

[vstinner]

configure.ac: Add PY_CHECK_FUNC_PRIVATE() function, similar to PY_CHECK_FUNC() but defines macro _Py_HAVE_xxx instead of HAVE_xxx.

Use PY_CHECK_FUNC_PRIVATE() for functions: acospi, asinpi, atanpi, atan2pi, cospi, sinpi and tanpi.

• Issue: The Python C API should only define macros with a name starting wit Py #157695

[skirpichev]

@vstinner, do you suggest to rename all macros, coming from standard configure tests like AC_CHECK_FUNCS_ONCE()?

I don't think that they pose some problems for programs, including Python.h: if people rely on configure macros - they should include own config.h after Python.h, that's all.

[vstinner]

My proposition in issue #157695 is to no longer add macros with a name which doesn't start with Py to the Python C API. So new macros must start with Py.