Avoid non-trivial global constants in SHA-NI code
This is a potential solution for #18456. It seems that the compiler cannot turn _mm_set_epi64x(<constant>,<constnant>) into a constant itself, and thus emits a global initializer for the MASK, INIT0, and INIT1 global constants in the sha-ni SHA256 implementation. Change this by turning them into dumb byte arrays, loading them into an SSE variable whenever needed. Tested on a SHA-NI capable machine. I do not observe any obvious performance impact (but this is hard to measure, it's already very fast...).
Backport of core PR18553.
cmake -GNinja .. -DENABLE_SSE41=OFF -DENABLE_AVX2=OFF ninja all check bench-bitcoin
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D6278