`align: 32` in `sha2` results in miscompilation

[arnetheduck]

Due to nim-lang/Nim#25457, using align:32 in sha2.nim is not supported.

The highest possible compatible alignment for refc depends on the platform, but can be seen in MDigest

An example crash due to this misalignment can be seen when running nimbus - the error specifically happens because when -march=native is enabled, a vmovdqa instruction is generated to init the context and the target pointer is not aligned sufficiently.