Fix allocation of low-alignment memory

Fix allocation of low-alignment memory

posix_memalign() returns EINVAL if the alignment argument is not a
multiple of sizeof(void*). Use regular malloc() for those cases.
malloc() is specified to allocate memory which is "suitably aligned for
any built-in type".

Bug b/128618202

Change-Id: Ibee07be89f2a5bd6be770c35710b20b0c752dfd1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27228
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>