avoid non-standard `__attribute__`, instead use C++ `alignas`

[bertwesarg]

See https://en.cppreference.com/w/cpp/language/alignas

Fixes #665

[devreal]

Seems like MaxElementTest.TestFindArrayDistributeBlockcyclic breaks:

[  RUN     ] MaxElementTest.TestFindArrayDistributeBlockcyclic
corrupted double-linked list

===================================================================================
=   BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
=   PID 2171 RUNNING AT 836828ca20fd
=   EXIT CODE: 134
=   CLEANING UP REMAINING PROCESSES
=   YOU CAN IGNORE THE BELOW CLEANUP MESSAGES
===================================================================================
YOUR APPLICATION TERMINATED WITH THE EXIT STRING: Aborted (signal 6)
This typically refers to a problem with your application.
Please see the FAQ page for debugging suggestions
[[   FAIL ]] 0 failed tests, returned 134

[bertwesarg]

Seems like MaxElementTest.TestFindArrayDistributeBlockcyclic breaks:

Is there a test, which only tests the alignment? If not, why wasn't there one added, with this file?