Try wasmer and lucet as alternatives to wasmtime

However:
- wasmer seems to have issues with signals, causing some tests to fail
- lucet's --dir option doesn't seem to work with relative paths

These are temporary limitations, that are likely to be fixed soon.

test/default/wasi-test-wrapper.sh

@@ -1,4 +1,11 @@
 #! /bin/sh
 
-wasmtime -o --dir=. "$1"
-
+if command -v wasmtime >/dev/null; then
+  wasmtime -o --dir=. "$1" && exit 0
+fi
+if command -v wasmer >/dev/null; then
+  wasmer run "$1" --dir=. && exit 0
+fi
+if command -v lucetc-wasi >/dev/null && command -v lucet-wasi >/dev/null; then
+  lucetc-wasi -o "${1}.so" --opt-level best "$1" && lucet-wasi "$1.so" && exit 0
+fi