testsuite: fix permission bits in copy_files

When the testsuite driver copy files instead of symlinking them, it
should also copy the permission bits, otherwise there'll be permission
denied errors. Also, enforce file copying when testing wasm32, since
wasmtime doesn't handle host symlinks quite well
(https://github.com/bytecodealliance/wasmtime/issues/6227).

(cherry picked from commit 791cce64)