Instead of the kernel heap being a compile-time parameter, make it
a runtime parameter (if DEBUG_HEAPS is specified, at least; otherwise
we're hardwired to the slab heap as before.)
This is similar to what's done in userland: there LD_PRELOAD and
MALLOC_DEBUG control the heaps, here "kernel_malloc" and then
"guarded_heap_options" kernel settings control the heap.
While at it, apply fixes to the guarded and debug heaps to ensure
a minimum alignment of sizeof(void*), if no specific alignment
is requested.
Tested with a lot of build configurations (DEBUG_HEAPS 0, 1;
DEBUG_HEAPS_DEFAULT slab, guarded; USE_DEBUG_HEAPS_FOR_OBJECT_CACHE
0, 1) and with various parameters specified in the bootloader.
Augustin Cavalier
a277043c1f