OpenBSD like FreeBSD uses stdlib.h not malloc.h

[jturner]

Trying to build wasmtime on OpenBSD noticed it's trying to pull in malloc.h. It should be using stdlib.h like FreeBSD. Unless you get to it first, I'll submit a MR shortly. Thanks

[seanm]

malloc.h is non-standard and obsolete, even on linux. It is required for some old functions like memalign but after looking over jitprofiling.c I don't see why it is needed, even on linux.

I think it can just be removed.