Fix building with go 1.16

The newly added platform `windows-arm64` isn't available on Go 1.16. In
fact, any unsupported "GOOS-GOARCH" pair should be skipped so that we
can keep adding platforms in the future without worrying about whether
the Go version that an extension author has chosen for their project
supports that platform.

build_and_release.sh

@@ -33,9 +33,15 @@ if [ -n "$GH_EXT_BUILD_SCRIPT" ]; then
   echo "invoking build script override $GH_EXT_BUILD_SCRIPT"
   ./"$GH_EXT_BUILD_SCRIPT" "$tag"
 else
+  IFS=$'\n' read -d '' -r -a supported_platforms < <(go tool dist list) || true
+
   for p in "${platforms[@]}"; do
     goos="${p%-*}"
     goarch="${p#*-}"
+    if [[ " ${supported_platforms[*]} " != *" ${goos}/${goarch} "* ]]; then
+      echo "warning: skipping unsupported platform $p" >&2
+      continue
+    fi
     ext=""
     if [ "$goos" = "windows" ]; then
       ext=".exe"