Add a portable XERBLA handler API

[moluopro]

After #5899 corrected the CTest registration, the Windows ARM64 shared-library job exposed failures in the xerbla_* extension tests: calls originating in the OpenBLAS DLL did not reach the test executable's xerbla override.

#5901 works around this Windows DLL symbol-resolution limitation by switching the CI job to a static build. This PR instead adds an explicit XERBLA handler API for shared-library users and tests, and prevents BLAS and CBLAS error-exit failures from passing silently.

Changes

• Adds openblas_set_xerbla, with handler replacement and NULL reset support.
• Preserves the Fortran ABI and ELF strong-symbol interposition while normalizing routine-name lengths.
• Preserves callback types in prefixed and suffixed installs without changing existing Windows export ordinals.
• Uses explicit handlers where interposition is unavailable and propagates BLAS and CBLAS test failures through CTest and Make.

[martin-frbg]

While this looks like a very interesting addition, it still bothers me that it appears to be "only" the utest_ext job that fails to bind the matching xerbla, while the regular BLAS/CBLAS tests appear to manage just fine.

[moluopro]

Good point. The regular BLAS/CBLAS tests had the same problem, but their failures were not propagated correctly.

I have prepared a fix and will push it shortly.