ir,build: pragma support (#97)

Adds support for arbitrary compiler directives.

Fixes #15

ir/ir.go

@@ -144,10 +144,17 @@ func (f *File) Functions() []*Function {
 	return fns
 }
 
+// Pragma represents a function compiler directive.
+type Pragma struct {
+	Directive string
+	Arguments []string
+}
+
 // Function represents an assembly function.
 type Function struct {
 	Name       string
 	Attributes attr.Attribute
+	Pragmas    []Pragma
 	Doc        []string
 	Signature  *gotypes.Signature
 	LocalSize  int
@@ -171,6 +178,14 @@ func NewFunction(name string) *Function {
 	}
 }
 
+// AddPragma adds a pragma to this function.
+func (f *Function) AddPragma(directive string, args ...string) {
+	f.Pragmas = append(f.Pragmas, Pragma{
+		Directive: directive,
+		Arguments: args,
+	})
+}
+
 // SetSignature sets the function signature.
 func (f *Function) SetSignature(s *gotypes.Signature) {
 	f.Signature = s