x86-64: Properly align La_x86_64_retval to VEC_SIZE [BZ #22715]

_dl_runtime_profile calls _dl_call_pltexit, passing a pointer to
La_x86_64_retval which is allocated on stack.  The lrv_vector0
field in La_x86_64_retval must be aligned to size of vector register.
When allocating stack space for La_x86_64_retval, we need to make sure
that the address of La_x86_64_retval + RV_VECTOR0_OFFSET is aligned to
VEC_SIZE.  This patch checks the alignment of the lrv_vector0 field
and pads the stack space if needed.

Tested with x32 and x86-64 on SSE4, AVX and AVX512 machines.  It fixed

FAIL: elf/tst-audit10
FAIL: elf/tst-audit4
FAIL: elf/tst-audit5
FAIL: elf/tst-audit6
FAIL: elf/tst-audit7

on x32 AVX512 machine.

(cherry picked from commit 207a72e2)

	[BZ #22715]
	* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_profile): Properly
	align La_x86_64_retval to VEC_SIZE.