The sample program in cranelift/filetests/src/function_runner.rs
would abort with an mprotect failure under certain circumstances,
see https://github.com/bytecodealliance/wasmtime/pull/4453#issuecomment-1303803222
Root cause was that enabling PROT_EXEC on the main process heap
may be prohibited, depending on Linux distro and version.
This only shows up in the doc test sample program because the main
clif-util is multi-threaded and therefore allocations will happen
on glibc's per-thread heap, which is allocated via mmap, and not
the main process heap.
Work around the problem by enabling the "selinux-fix" feature of
the cranelift-jit crate dependency in the filetests. Note that
this didn't compile out of the box, so a separate fix is also
required and provided as part of this PR.
Going forward, it would be preferable to always use mmap to allocate
the backing memory for JITted code.
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