Introduce libc_aligned.so for evbppc-powerpc32, which provides
strictly-aligned versions of memcmp(3), bcopy(3), memcpy(3), and
memmove(3).

This is used for 403 by ld.so.conf with machdep.no_unaligned variable.

With this library, unaligned memory accesses are significantly reduced
for 403 (from several hundreds to few tens per sec under heavy load);
only ld.elf_so (typically few times per fork) and statically-linked
binaries do such access.