elf: Add SVE support for aarch64 rtld-auditazanella/ld-audit-fixes

To implement lazy binding is enabled when profiling or auditing used,
even when STO_AARCH64_VARIANT_PCS is set.  Also, to not incur in
performance penalties on architecture without SVE, the PLT entrypoint
is set to a newer one, _dl_runtime_profile_sve, which is used iff
'hwcap' has HWCAP_SVE bit set.

This should be a fair assumption since SVE has a defined set of
registers for argument passing and return values.  A new ABI with either
different argument passing or different registers would require a
different PLT entry, but I assume this would require another symbol flag
anyway (or at least a different ELF mark to indicate so).

The profile '_dl_runtime_profile_sve' entrypoint assumes the largest SVE
register size possible (2048 bits) and thus it requires a quite large
stack (8976 bytes).  I think it would be possible make the stack
requirement dynamic depending of the vector length, but it would make
the PLT audit function way more complex.

It extends the La_aarch64_vector with a long double pointer to a stack
alloced buffer to hold the SVE Z register, along with a pointer to hold
the P registers on La_aarch64_regs.

It means the if 'lr_sve' is 0 in either La_aarch64_regs or
La_aarch64_retval the La_aarch64_vector contains the floating-pointer
registers that can be accessed directly (non SVE hardware).  Otherwise,
'La_aarch64_vector.z' points to a memory area that holds up to 'lr_sve'
bytes for the Z registers, which can be loaded with svld1 intrinsic for
instance (as tst-audit28.c does).  The P register follows the same
logic, with each La_aarch64_regs.lr_sve_pregs pointing to an area of
memory 'lr_sve/8' in size.

So, to access the FP register as float you can use:

 static inline float regs_vec_to_float (const La_aarch64_regs *regs,
				        int idx)
 {
   float r;
   if (regs->lr_sve == 0)
     r = regs->lr_vreg[idx].s;
   else
     memcpy (&r, &regs->lr_vreg[idx].z[0], sizeof (r));
   return r;
 }

This patch is not complete yet: the tst-audit28 does not check if
compiler supports SVE (we would need a configure check to disable for
such case), I need to add a proper comment for the
_dl_runtime_profile_sve stack layout, the test need to check for the P
register state clobbering.

I also haven't check the performance penalties with this approach, and
maybe the way I am saving/restoring the SVE register might be optimized.

In any case, I checked on a SVE machine and at least the testcase work
as expected without any regressions.  I also did a sniff test on a non
SVE machine.

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