feature: add buildmode=wasi-legacy to support existing base of users who expected the

older behavior for wasi modules to not return an exit code as if they were reactors.

See #4726 for some details on what this is intended to address.

Signed-off-by: deadprogram <ron@hybridgroup.com>

builder/build.go

@@ -672,6 +672,16 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 		ldflags = append(ldflags, "--no-entry")
 	}
 
+	if config.Options.BuildMode == "wasi-legacy" {
+		if !strings.HasPrefix(config.Triple(), "wasm32-") {
+			return result, fmt.Errorf("buildmode wasi-legacy is only supported on wasm")
+		}
+
+		if config.Options.Scheduler != "none" {
+			return result, fmt.Errorf("buildmode wasi-legacy only supports scheduler=none")
+		}
+	}
+
 	// Add compiler-rt dependency if needed. Usually this is a simple load from
 	// a cache.
 	if config.Target.RTLib == "compiler-rt" {