Fix declaration order in external BLAS/LAPACK interfaces

[Chaitanya-970]

Fixes #1210.

With external BLAS/LAPACK enabled, gfortran rejects some interfaces under -std=f2018 because arrays are declared before the integer arguments used in their bounds. This moves those integer declarations ahead of the arrays without changing the procedure signatures.

CI now includes a GCC 14 Release build with external BLAS/LAPACK, followed by a separate -std=f2018 compilation check of the external interface modules. Library discovery is required so the job cannot silently fall back to the bundled implementation.

This also fixes the bare dl entry in the generated pkg-config file, which was preventing Linux CI from linking its smoke test. The same issue is covered by #1220.

Tested with gfortran 15.3.1:

• The patched external interface modules compile under -std=f2018, as do the isolated 64-bit external interface declarations.
• A build linked against real OpenBLAS/LAPACK succeeds.
• Both bundled and external test suites finish with zero failures across 433 tests, with one skipped in each suite.

The external suite was run serially after a parallel run hit shared-file interference in the loadtxt example. The separate GCC 15 compatibility problems covered by #1209 are outside this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.44%. Comparing base (f47e1b3) to head (e011ebf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1221      +/-   ##
==========================================
- Coverage   69.52%   69.44%   -0.08%     
==========================================
  Files          20       20              
  Lines        2556     2556              
==========================================
- Hits         1777     1775       -2     
- Misses        779      781       +2     

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