sysconfig.get_platform on arm64 does not contain 'ARM'

[jeremyd2019]

From msys2/MINGW-packages#20569
cmake attempts to verify that python is targeting arm with the following:

      execute_process (COMMAND ${launcher} "${_${_PYTHON_PREFIX}_EXECUTABLE}" -c
        "import sys, sysconfig; sys.stdout.write(sysconfig.get_platform())"
        RESULT_VARIABLE result
        OUTPUT_VARIABLE platform
        ERROR_QUIET
        OUTPUT_STRIP_TRAILING_WHITESPACE)
      string(TOUPPER "${platform}" platform)
      if (result OR ((target_arm AND NOT platform MATCHES "ARM") OR
                     (NOT target_arm AND platform MATCHES "ARM")))
        # interpreter not usable or has wrong architecture

In the case of this fork, sysconfig.get_platform() returns mingw_aarch64, not mingw_arm64 or something similar. I'm not sure whether this should be patched here (probably as part of the 3.12 update), or in cmake (to check for MATCHES "ARM|AARCH" instead) but I wanted to open an issue for it here so it wouldn't be forgotten for 3.12

[MehdiChinoune]

CMake is already patched https://github.com/msys2/MINGW-packages/blob/f7ef8517/mingw-w64-cmake/0003-fix-find-python-on-mingw-aarch64.patch

[jeremyd2019]

ok, then this issue can just be to decide if we want to take the opportunity to switch the platform to contain arm or rely on continuing to patch cmake.

[lazka]

If aarch64 would be removed we'd have to update the detection in meson: https://github.com/mesonbuild/meson/blob/1a458aacb407e3893b7e832a7a3f75e581c5e3f4/mesonbuild/dependencies/python.py#L196-L204

[jeremyd2019]

if one or the other would have to be patched, it may be best not to change it