misc: Appease gcc 5.1

misc: Appease gcc 5.1

Three minor issues are resolved:

1. Apparently gcc 5.1 does not like negation of booleans followed by
   bitwise AND.

2. Somehow the compiler also gets confused and warns about
   NoopMachInst being unused (removing it causes compilation errors
   though). Most likely a compiler bug.

3. There seems to be a number of instances where loop unrolling causes
   false positives for the array-bounds check. For now, switch to
   std::array. Potentially we could disable the warning for newer gcc
   versions, but switching to std::array is probably a good move in
   any case.