crypto/mem.c: don't use aligned_alloc in CRYPTO_aligned_alloc

crypto/mem.c: don't use aligned_alloc in CRYPTO_aligned_alloc

The original C11 specification is pretty weird: it specifies that the size
must be a multiple of alignment (rendering it useless for small page-aligned
allocations that, for example, might be useful for RDMA) and until DR460[1]
it was UB in failing to do so (as it is with OPENSSL_ligned_alloc() calls
in alloc_new_neighborhood_list() on 32-bit systems, for example).
Moreover, it has arguably not been used much before, as all supported POSIX
systems have at least POSIX 2001 compatibility level nowadays,
Windows doesn't implement aligned_alloc() at all (because implementation
of free() in MS CRT is unable to handle aligned allocations[2]),
and _ISOC11_SOURCE is a glibc-specific feature test macro.

[1] https://open-std.org/JTC1/SC22/WG14/www/docs/summary.htm#dr_460
[2] https://learn.microsoft.com/en-us/cpp/standard-library/cstdlib?view=msvc-170#remarks-6

Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28059)