MAINT: remove redundant open() modes and io.open() alias

This fixes a bug in distutils that prevented the use of the C++ linker
needed to link _multiarray_umath.

Fixes #23595

* BUILD: update OpenBLAS to 0.3.21 and clean up openblas download test

* set LDFLAGS on windows64 like the openblaslib build does

* use rtools compilers on windows when building wheels

* fix typos

* add rtools gfortran to PATH

* use the openblas dll from the zip archive without rewrapping

* typos

* copy dll import library for 64-bit interfaces

* revert many of the changes to azure-steps-windows.yaml, copy openblas better in wheels

* fix wildcard copy

* test OpenBLAS build worked with threadpoolctl

* typos

* install threadpoolctl where needed, use for loop to recursively copy

* update macos OpenBLAS suffixes for newer gfortran hashes

* use libgfortran5.dylib on macos

* fix scripts

* re-use gfortran install from MacPython/gfortran-install on macos

* use pre-release version of delocate

* fixes for wheel builds/tests

* add debugging cruft for pypy+win, macos wheels

* add DYLD_LIBRARY_PATH on macosx-x86_64

* use 32-bit openblas interfaces for ppc64le tests

* skip large_archive test that sometimes segfaults on PyPy+windows

Remove reference to Visual Studio version required by old versions
of Python. Python >= 3.5 is built with Microsoft Visual C++ 14.0 /
Visual Studio 2015:
	https://wiki.python.org/moin/WindowsCompilers

Numpy extensions define the extra_cxx_compile_args and extra_c_compile_args
filed, but distutils extensions don't. Take that into account when populating
build_extension.

Should fix #20928

In SciPy we had a couple of cases where we build a Python extension
with C source files but linked against static libraries built from
Fortran code. Those should be using the Fortran linker, but this
was broken in 1.22.0 by gh-19713 (the PR that introduced C++ in NumPy).

This fixes a few issues in the `build_ext` command, and documents better
what is going on there.

Should close SciPy issues 8325 and 15414.