Add a portable XERBLA handler API

[moluopro]

After #5899 fixed the CTest registration so that openblas_utest_ext ran the correct executable, the Windows ARM64 shared-library job exposed failures in the xerbla_* extension tests: some calls from the OpenBLAS DLL reached its normal XERBLA implementation instead of the test executable's override.

#5901 works around this Windows DLL symbol-resolution limitation by switching that CI job to a static build. This PR instead adds an explicit XERBLA handler API, giving shared-library users and tests a reliable mechanism that does not depend on link-time symbol interposition.

Changes

• Adds openblas_set_xerbla for installing a process-wide handler, returning the previous handler, and restoring the default with NULL.
• Preserves the Fortran XERBLA ABI and ELF strong-symbol interposition.
• Normalizes routine-name lengths and bounds the default error output.
• Prevents SYMBOLPREFIX and SYMBOLSUFFIX from mangling callback types in CMake and Make installs without changing existing Windows export ordinals.
• Uses explicit handlers in tests and makes CBLAS error-exit mismatches return a failure status.