Setting MALLOC_XMALLOC enables a runtime toggle that allows to make allocations abort() on OOM instead of returning NULL. In other words, it enables a toggle that allows to turn all allocations into infallible allocations. The toggle however still defaults to being disabled, which means even when MALLOC_XMALLOC is defined when building mozjemalloc, there is no change in behavior, unless a MALLOC_OPTIONS is set. Even if this were useful to anyone (MALLOC_XMALLOC is only defined on debug builds, limiting the usefulness), this is something replace-malloc, in Firefox, is meant to be used for. So let's remove this feature, and possibly add an equivalent replace-malloc later if deemed necessary. Review commit: https://reviewboard.mozilla.org/r/145120/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/145120/