[llgo] irgen: expose PackageCreated hook

[axw]

LGTM

irgen/compiler.go

type CompilerOptions struct {
   // Importer is the importer. If nil, the compiler will set this field
   // automatically using MakeImporter().
   Importer types.Importer
 
   // InitMap is the init map used by Importer. If Importer is nil, the
   // compiler will set this field automatically using MakeImporter().
   // If Importer is non-nil, InitMap must be non-nil also.
   InitMap map[*types.Package]gccgoimporter.InitData
+
+  // PackageCreated is a hook passed to the go/loader package via
+  // loader.Config, see the documentation for that package for more
+  // information.
+  PackageCreated func(*types.Package)
 }
 
 type Compiler struct {
   opts       CompilerOptions
   dataLayout string
   pnacl      bool
 }
 
func (compiler *compiler) compile(fset *token.FileSet, astFiles []*ast.File, importpath string) (m *Module, err error) {
   }
 
   impcfg := &loader.Config{
     Fset: fset,
     TypeChecker: types.Config{
       Import: compiler.Importer,
       Sizes:  compiler.llvmtypes,
     },
-    Build: &buildctx.Context,
+    Build:          &buildctx.Context,
+    PackageCreated: compiler.PackageCreated,
   }
   // If no import path is specified, then set the import
   // path to be the same as the package's name.
   if importpath == "" {
     importpath = astFiles[0].Name.String()
   }
   impcfg.CreateFromFiles(importpath, astFiles...)
   iprog, err := impcfg.Load()