elf: Fix runtime linker auditing on aarch64 (BZ #26643)

The dynamic linker's auditing was not working on aarch64. There were
two distinct problems:

  1. _dl_runtime_resolve was not preserving x8 the indirect result
     location  register.

  2. The NEON Q registers pushed onto the stack by _dl_runtime_resolve()
     were twice the size of D registers extracted from the stack frame by
     _dl_runtime_profile().

To fix it the rtld-auditor interfaces is changed for aarch64:

  * LAV_CURRENT is bumped to v2 and loader will fail to load audit
    modules that return a version different than the one supported.

  * The La_aarch64_regs structure was expanded to include x8 and the
    full sized NEON V registers that are required to be preserved by the
    ABI.

  * dl_runtime_profile needed to extract registers saved by
    _dl_runtime_resolve and put them into the new correctly sized
    La_aarch64_regs structure.

  * The return value structure La_aarch64_retval also did not have the
    correctly sized NEON V registers.

Similar to x86, a new La_aarch64_vector type to represent the NEON
register is added on the La_aarch64_regs (so each type can be accessed
easier).

Checked on aarch64-linux-gnu.

Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

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