Fix i386 "softfloat" bug

See https://golang.org/issues/44500 for details (tldr, Go 1.16 changes "GO386" from "387" to "softfloat" but the bootstrap compiler isn't 1.16 yet so balks at the changed value).

This also makes our "compilation" much more explicit by explicitly noting the "env" needed to build each bashbrew architecture we support and embedding those directly.

(I've also added "i386" to GitHub Actions, which will double our matrix size, but will hopefully help us catch issues like this in the future.)

Author: tianon

.github/workflows/ci.yml

@@ -24,6 +24,7 @@ jobs:
         run: |
           git clone --depth 1 https://github.com/docker-library/bashbrew.git -b master ~/bashbrew
           strategy="$(~/bashbrew/scripts/github-actions/generate.sh)"
+          strategy="$(~/bashbrew/scripts/github-actions/munge-i386.sh -c <<<"$strategy")"
           jq . <<<"$strategy" # sanity check / debugging aid
           echo "::set-output name=strategy::$strategy"