GOARM, goARMChanged         = EnvOrAndChanged("GOARM", fmt.Sprint(buildcfg.GOARM))
	GO386, go386Changed         = EnvOrAndChanged("GO386", buildcfg.GO386)
	GOAMD64, goAMD64Changed     = EnvOrAndChanged("GOAMD64", fmt.Sprintf("%s%d", "v", buildcfg.GOAMD64))
	GOMIPS, goMIPSChanged       = EnvOrAndChanged("GOMIPS", buildcfg.GOMIPS)
	GOMIPS64, goMIPS64Changed   = EnvOrAndChanged("GOMIPS64", buildcfg.GOMIPS64)

	if cfg.Goarch == "386" {
		// Define GO386_value from cfg.GO386.
		args = append(args, "-D", "GO386_"+cfg.GO386)
	}

	if cfg.Goarch == "amd64" {
		// Define GOAMD64_value from cfg.GOAMD64.
		args = append(args, "-D", "GOAMD64_"+cfg.GOAMD64)
	}

	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
		// Define GOMIPS_value from cfg.GOMIPS.
		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)
	}

For GOARCH=amd64, arm, ppc64, ppc64le, and riscv64, a particular feature level
sets the feature build tags for all previous levels as well.
For example, GOAMD64=v2 sets the amd64.v1 and amd64.v2 feature flags.
This ensures that code making use of v2 features continues to compile
when, say, GOAMD64=v4 is introduced.
Code handling the absence of a particular feature level
should use a negation:

	//go:build !amd64.v2