Rebuild for flang 19

[regro-cf-autotick-bot]

This PR has been triggered in an effort to update flang19.

Notes and instructions for merging this PR:

1. Please merge the PR only after the tests have passed.
2. Feel free to push to the bot's branch to update this PR if needed.

Please note that if you close this PR we presume that the feedstock has been rebuilt, so if you are going to perform the rebuild yourself don't close this PR until the your rebuild has been merged.

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Here are some more details about this specific migrator:

TL;DR: We are trying to switch our Fortran compilers on windows to flang.
This is not 100% guaranteed to work, but should be fine in the majority of cases.

The new LLVM-based flang has become mature enough that it should be possible to
broadly switch over our Fortran compilers on windows to it (until now we only had
an ancient pre-LLVM flang 5, or alternatively the GCC-based m2w64_fortran).

As such, this PR attempts to homogenize any use of m2w64_fortran and other m2w64_*
compilers to our default stack (which would then be MSVC + flang on windows), with
the exception of feedstocks for R-packages, which stay on the m2w64_ compilers.

Recipes that have hard-coded expectations about the name of the fortran compiler
will need to adjust to use %FC% or flang-new for the compiler name. Similarly,
you may need to change the linker to %LD% or use lld-link.

It is also possible that you run into compilation errors due to differences in
compiler behaviour, bugs or as-yet unimplemented features. In case of compilation
errors due to stricter default language standards, you should be able to fix things
by passing -std=legacy to FFLAGS.

If you have problems with this PR, feel free to ping the @c-f/flang-activation team.
In case you have convinced yourself that flang really is not ready yet to be used to
compile a given feedstock, you may also close this migrator PR.

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If this PR was opened in error or needs to be updated please add the bot-rerun label to this PR. The bot will close this PR and schedule another one. If you do not have permissions to add this label, you can use the phrase @conda-forge-admin, please rerun bot in a PR comment to have the conda-forge-admin add it for you.

_{This PR was created by the regro-cf-autotick-bot. The regro-cf-autotick-bot is a service to automatically track the dependency graph, migrate packages, and propose package version updates for conda-forge. Feel free to drop us a line if there are any issues! This PR was generated by https://github.com/regro/cf-scripts/actions/runs/11669226258 - please use this URL for debugging.}

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found some lint.

Here's what I've got...

For recipe/meta.yaml:

• You're setting a constraint on the __osx virtual package directly; this should now be done by adding a build dependence on {{ stdlib("c") }}, and overriding c_stdlib_version in recipe/conda_build_config.yaml for the respective platform as necessary. For further details, please see META: {{ stdlib("c") }} migration conda-forge.github.io#2102.
• In your conda_build_config.yaml, please change the name of MACOSX_DEPLOYMENT_TARGET, to c_stdlib_version!

For recipe/meta.yaml:

• In conda-forge.yml: $.build_with_mambabuild = False.

  'Build With Mambabuild' is deprecated.
  build_with_mambabuild is deprecated, use conda_build_tool instead.

  Schema

  {
    "anyOf": [
      {
        "type": "boolean"
      },
      {
        "type": "null"
      }
    ],
    "default": true,
    "deprecated": true,
    "title": "Build With Mambabuild"
  }

[h-vetinari]

Let's decide if/how to switch in #249 first

[xhochy]

See #257