This adds a very minimal internal allocator api that lets us create a
dynamically growable (grow only) stack.
Underlying the allocator is the idea of "sub stacks" which are simply
malloc()'d chunks of memory kept in a linked list. The stack itself
maintains a pointer to the current sub-stack and a current
sub-stack-offset. 99% of the time allocating from the stack is just a
case of returning a pointer to the current sub-stack + sub-stack-offset
and bumping the offset by the allocation size. If there isn't room in
the current sub-stack then we walk through the list of free sub-stacks
looking for one that's big enough for the allocation and if we reach the
end of the list then we allocate a new sub-stack twice as big as the
last (or twice as big as the requested allocation if that's bigger).
Since it's a stack model there is no api to free allocations, just a
function to rewind the stack to the beginning.
We expect this to be useful in multiple places in Cogl as an extremely
fast allocator in cases when we know we can scrap all the allocations
after we're done figuring something out or as a building block for
other allocators.
For example the tessellator used for CoglPath allocates lots of tiny
structures that can all be freed after tessellation.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 6ee4a7a1b7f695bdfeb10ffa4112e776beea0a9d)
