internal/rosa: respect preferred loadavg target

This generally improves build performance and system responsiveness.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/make.go

@@ -160,7 +160,8 @@ func (attr *MakeHelper) script(t Toolchain, name string) string {
 
 	scriptMake := `
 make \
-	` + jobsFlagE
+	` + jobsFlagE + ` \
+	` + loadFlagE
 	if len(attr.Make) > 0 {
 		scriptMake += " \\\n\t" + strings.Join(attr.Make, " \\\n\t")
 	}
@@ -170,6 +171,7 @@ make \
 		(!attr.SkipCheckEarly || !t.stage.isStage0()) {
 		scriptMake += attr.ScriptCheckEarly + `make \
 	` + jobsFlagE + ` \
+	` + loadFlagE + ` \
 	`
 		if len(attr.Check) > 0 {
 			scriptMake += strings.Join(attr.Check, " \\\n\t")