Implement optimization strategy for normalized booleans

[boriel]

What / Why

Now that automatic boolean normalization is implemented, we need it to follow one of these two strategies:

• Optimization for speed (spends more memory)
• Optimization for size (saves memory at the cost of some penalization in speed)
• Auto (the default), tries to optimize always following a sensible default, for speed.

Some subroutines (i.e. string comparison and float comparison) are already normalized. But other ones, notability 16 and 32 bits comparison needs to be defined and implemented for size strategy.

The macro __ZXB_OPT_STRATEGY will be defined according to the strategy.