malloc: Improve aligned_alloc and calloc test coverage.

malloc: Improve aligned_alloc and calloc test coverage.

Add a DSO (malloc/tst-aligned_alloc-lib.so) that can be used during
testing to interpose malloc with a call that randomly uses either
aligned_alloc, __libc_malloc, or __libc_calloc in the place of malloc.
Use LD_PRELOAD with the DSO to mirror malloc/tst-malloc.c testing as an
example in malloc/tst-malloc-random.c.  Add malloc/tst-aligned-alloc-random.c
as another example that does a number of malloc calls with randomly sized,
but limited to 0xffff, requests.

The intention is to be able to utilize existing malloc testing to ensure
that similar allocation APIs are also exposed to the same rigors.

Reviewed-by: DJ Delorie <dj@redhat.com>