Add CI targets, fix test_std.js (#247)

Add CI targets, fix test_std.js (#247)

This switches the exec test to `SIGTERM` rather than `SIGQUIT` since the
latter didn’t seem to work in QEMU, and the distinction doesn’t really
matter for this test.

This also makes the `isatty()` check smarter by checking whether `STDIN`
is, in fact, a terminal.

Added qemu-alpine targets i386, arm32v6, arm32v7, arm64v8, s390x

Co-authored-by: Felipe Gasper <felipe@felipegasper.com>