AVX512 gcc fix

Only use the AVX512 version of memswap when compiling with the Intel compiler as GCC seems to produce invalid code.

Also allocate the offset arrays using an aligned allocation.

Fixes #428 (closed) and #430 (closed).

mentioned in issue #430 (closed)

Thanks, all looks like what we need. I'll give this a test.

LGTM!

assigned to @pdraper

Ran an EAGLE_50 test all night so I'm happy this fixes the problem. Accepting.

mentioned in commit 85af3e05

merged