In emscripten's libc++ port, operator new takes a size_t (unsigned int). However, when using the wasm backend, clang is not pleased, and says "no, that must be a size_t (unsigned long)",

error: 'operator new' takes type size_t ('unsigned long') as first parameter

This blocks many (all?) tests using c++ STL stuff.

What's going on here?

cc @sunfishcode @jfbastien @dschuff