Make sure that alignTableMem() always aligns to an 8 byte boundary
on 64-bit architectures where this is the usual size of pointers.
Also make sure that loadTextIntoMem() always calls alignTableMem().
This has been tested on OpenBSD/loongson (a mips64el architecture which requires
strict alignment), with clang++ 8.0.1 and simon2-cd-fr.
Fixes bug #6220.