changed behaviour of malloc(0) and optimized calloc

[ZERICO2005]

calloc (when __TICE__ is defined) now uses an inlined implementation of bzero which uses the $E40000 address to speed up the zero filling of memory.

Otherwise, it will use the previous memset implementation when __TICE__ is undefined.

[runer112]

Seems like the add here should never carry?

Suggested change

	add hl, bc
	or a, a
	sbc hl, bc
	add hl, bc
	sbc hl, bc

[calc84maniac]

Only if you also move up the pop of the size (the pop of the parameter is undefined data because malloc may clobber it)

[ZERICO2005]

does this go off the assumption that malloc won't return an address higher than 0xE40000 on the CE and that the allocation size is less than 0x1C0000 bytes or etc

[runer112]

This relies on the seemingly sound assumption that the pointer to the allocated memory plus the allocation size does not overflow.

[ZERICO2005]

I assume it is okay for cpd to read nonnull_ptr_from_malloc + size

[ZERICO2005]

To reduce the complexity of this PR, I undid the allocator switches to nonzero_fill_calloc when malloc(0) is known to return NULL commits for now (which essentially added 4 different calloc variants). That way we can focus on the two important changes that will be made in this PR:

• Changing the behavior of __simple_malloc(0) and __standard_malloc(0) to return NULL.
• Optimizing calloc zero filling by using the $E40000 all zeros address