[libc] Implement placeholder memory functions on the GPU (#101082)

Summary:
These functions are needed for `libc++` to link successfully. We can't
implement them well currently, so simply provide

[libc] Implement placeholder memory functions on the GPU (#101082)

Summary:
These functions are needed for `libc++` to link successfully. We can't
implement them well currently, so simply provide some stand-in
implementations. `realloc` will currently copy garbage and potentially
fault and `aligned_alloc` will work unless your alignment is more than
4K alignment. However, these should work in practice to get tests
running. I will write a real allocator soon™.

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