[lucet-runtime-internals] Call MAP_ANON mmap with fd -1

Linux is not strict on this, but e.g. FreeBSD is.

Author: valpackett

lucet-runtime/lucet-runtime-internals/src/region/mmap.rs

@@ -348,7 +348,7 @@ impl MmapRegion {
                     region.limits.total_memory_size(),
                     ProtFlags::PROT_NONE,
                     MapFlags::MAP_ANON | MapFlags::MAP_PRIVATE,
-                    0,
+                    -1,
                     0,
                 )?
             }