C++, no exceptions, and OOM in `operator new`

This example program is intended to allocate 4 wasm pages of memory:

#include <vector>
#include <stdio.h>

int main() {
  std::vector<int> v;
  for (int i = 0; i < 65536; i++) {
    v.push_back(4);
  }
}

This can be compiled to have a max wasm memory size of 2 pages, though, which will cause the program to OOM at runtime:

$ clang++ foo.cpp -o foo.wasm -O2 -Wl,--stack-first,--max-memory=131072 -fno-exceptions

which produces foo.wasm.gz.

When run:

$ wasmtime run ./foo.wasm

this program will (currently for me) infinite loop.

The issue seems to be that when compiled with -fno-exceptions, which I believe is currently required of C++ code compiled with wasi-libc to wasm since __cxa_throw isn't otherwise defined, then the operator new operator is defined to return NULL for failed allocations. For a native platform this is fine because it probably faults quickly when accessing this address. For Wasm, however, this is a valid address so the program keeps going.

This was, for me, an unfortunately slow way for me to discover that the original program I was working with was OOM-ing and needed a --max-memory argument to be passed that was larger than the base. I'm not sure how best to improve this, though, since I suspect aborting on failure would not be spec-compliant with C++.

Reproduce the failure with the provided C++ example, clang++ command, and wasmtime invocation. Start by tracing operator new under -fno-exceptions and the interaction with __cxa_throw, then determine a standards-compliant failure behavior for WebAssembly. Done means the OOM case no longer loops indefinitely and has a regression test covering the constrained-memory example.