configure: Make script more amenable to dodgy shells
configure: Make script more amenable to dodgy shells

Strict POSIX shells, and stripped-down shells (e.g. dash, busybox) may
not handle here-documents very gracefully, so do not rely on them. Also,
do not use the process-id expansion "$$".

aperezdc/lua-eol,aperezdc/lua-eol,aperezdc/eris,aperezdc/eris