[OpenMP] Basic BumpAllocator for (AMD)GPUs (#69806)

The patch contains a basic BumpAllocator for (AMD)GPUs to allow us to
run more tests. The allocator implements `malloc`, both internally and
externally, while we continue to default to the NVIDIA `malloc` when we
target NVIDIA GPUs. Once we have smarter or customizable allocators we
should consider this choice, for now, this allocator is better than
none. It traps if it is out of memory, making it easy to debug. Heap
size is configured via `LIBOMPTARGET_HEAP_SIZE` and defaults to 512MB.
It allows to track allocation statistics via
`LIBOMPTARGET_DEVICE_RTL_DEBUG=8` (together with
`-fopenmp-target-debug=8`). Two tests were added, and one was enabled.

This is the next step towards fixing
 https://github.com/llvm/llvm-project/issues/66708