[patch, Fortran] Implement -fexternal-blas64, PR 121161

[Steve Kargl]

On Tue, Sep 16, 2025 at 10:10:16PM +0200, Thomas Koenig wrote:
> Hello world,
> 
> the attached patch implements a new option, -fexternal-blas64,
> so people can use 64-bit libraries for external BLAS, like Intel
> MKL.
> 
> Regression-tested. OK for trunk?
> 

Thanks.  I've read through the patch, and it looks fine.
Feel free to commit.

-- 
Steve