Allocator that just uses malloc and bypasses custom jemalloc/freelist

[cmcfarlen]

This PR reimplements Allocator to just use malloc/free and completely ignores the ink_freelist code. It doesn't disable ProxyAllocator freelists. This means the -F (proxy allocator disable) works, but -f (disable freelist) does nothing.

This differs from the -f option (when jemalloc is enabled) in the following ways:

• honors advice and calls (jemalloc's) madvise (for nodump support on io buffers).
• Does not use the jemallocnodumallocator for aligned allocation, but uses (jemalloc's) aligned_alloc.
• does not use posix_madvise, or posix_memalign in any case

To use this allocator, one must pass --enable-malloc-allocator to configure otherwise it will behave as it always has.

[duke8253]

So if I'm understanding this correct, this is mostly for when jemalloc is around and we don't want to use the nodumpallocator. And if ats isn't built with jemalloc, this behaves the same as passing -f, other than the memalign part.

[cmcfarlen]

Yes, this shows a modest performance increase over -f but a huge increase over using ink_freelist* yet still honors madvise. Basically it is totally relying on the malloc implementation to do something performant and allows full tuning to that end.

Since this just uses the standard C memory calls, it would work with mimalloc as well but might have to include the overrides header.

[duke8253]

looks good to me.