Bugfix with temporary terms in block+bytecode

There were actually two distinct bugs, leading to incorrect results in some
corner cases:

– in the “evaluate” mode of the bytecode MEX, the temporary terms of the
  derivatives “evaluate” blocks were not evaluated at runtime; but these
  temporary terms may be needed for residuals of subsequent blocks;

– when the bytecode MEX was only computing residuals of the model (and not 1st
  order derivatives), the temporary terms of the derivatives were not evaluated
  at runtime; but these temporary terms may be needed for residuals of subsequent
  blocks.

(manually cherry picked from commit a97a41f6)