Fix which command check

The function have_witch failed because which is an alias in my environment.

This change makes the function work even if which command is an alias.

build_odin.sh

@@ -157,7 +157,7 @@ run_demo() {
 }
 
 have_which() {
-	if ! [ -x "$(command -v which)" ]; then
+	if ! command -v which 2>&1 ; then
 		panic "Could not find \`which\`"
 	fi
 }