ast,printer: add Includes field to File

Updates #12

ast.go

@@ -94,11 +94,14 @@ type Section interface {
 
 // File represents an assembly file.
 type File struct {
+	Includes []string
 	Sections []Section
 }
 
 func NewFile() *File {
-	return &File{}
+	return &File{
+		Includes: []string{"textflag.h"},
+	}
 }
 
 func (f *File) AddSection(s Section) {

printer/goasm.go

@@ -23,6 +23,7 @@ func NewGoAsm(cfg Config) Printer {
 
 func (p *goasm) Print(f *avo.File) ([]byte, error) {
 	p.header()
+	p.includes(f.Includes)
 	for _, s := range f.Sections {
 		switch s := s.(type) {
 		case *avo.Function:
@@ -38,13 +39,17 @@ func (p *goasm) Print(f *avo.File) ([]byte, error) {
 
 func (p *goasm) header() {
 	p.Comment(p.cfg.GeneratedWarning())
-	p.NL()
-	p.include("textflag.h")
 }
 
-func (p *goasm) include(path string) {
+func (p *goasm) includes(paths []string) {
+	if len(paths) == 0 {
+		return
+	}
+	p.NL()
+	for _, path := range paths {
 		p.Printf("#include \"%s\"\n", path)
 	}
+}
 
 func (p *goasm) function(f *avo.Function) {
 	p.NL()