main: use tags parser from buildutil

This should add support for things like quotes around tags, if they are
ever needed.

Only making this change now because I happened to stumble across
buildutil.TagsFlag.

compileopts/config.go

@@ -73,9 +73,7 @@ func (c *Config) BuildTags() []string {
 	for i := 1; i <= c.GoMinorVersion; i++ {
 		tags = append(tags, fmt.Sprintf("go1.%d", i))
 	}
-	if extraTags := strings.Fields(c.Options.Tags); len(extraTags) != 0 {
-		tags = append(tags, extraTags...)
-	}
+	tags = append(tags, c.Options.Tags...)
 	return tags
 }
 

compileopts/options.go

@@ -38,7 +38,7 @@ type Options struct {
 	PrintSizes      string
 	PrintAllocs     *regexp.Regexp // regexp string
 	PrintStacks     bool
-	Tags            string
+	Tags            []string
 	WasmAbi         string
 	GlobalValues    map[string]map[string]string // map[pkgpath]map[varname]value
 	TestConfig      TestConfig