[WIP] newt: Use default linker script if it's not specified in bsp.yml

Now if "bsp.linkerscript" key is empty default linker script
will be passed to the linker.

IMPORTANT: bsp.linkerscript key still has to be present in the
bsp.yml file. It simply has to exist without any paths specified.
It's done this way to prevent adding linker scripts to
native target's builds.

newt/pkg/bsp_package.go

@@ -82,6 +82,16 @@ func (bsp *BspPackage) resolvePathSetting(
 	return path, nil
 }
 
+func (bsp *BspPackage) getAutogeneratedLinkerScriptPath() (string, error) {
+	defaultLinkerScriptPath := "bin/" + bsp.yov.Pkg.Name() + "/generated/link/mynewt.ld"
+	proj := interfaces.GetProject()
+	path, err := proj.ResolvePath(proj.Path(), defaultLinkerScriptPath)
+	if err != nil {
+		return "", err
+	}
+	return path, nil
+}
+
 // Interprets a setting as either a single linker script or a list of linker
 // scripts.
 func (bsp *BspPackage) resolveLinkerScriptSetting(
@@ -103,14 +113,33 @@ func (bsp *BspPackage) resolveLinkerScriptSetting(
 			return nil, err
 		}
 
-		if path != "" {
+		if path == "autogenerated" {
+			path, err = bsp.getAutogeneratedLinkerScriptPath()
+			if err != nil {
+				return nil, util.PreNewtError(err,
+					"Could not resolve autogenerated linker script path for target \"%s\"",
+					bsp.yov.Pkg.Name())
+			}
+			paths = append(paths, path)
+		} else if path != "" {
 			paths = append(paths, path)
 		}
 	} else {
 		proj := interfaces.GetProject()
 
 		// Read each linker script from the list.
 		for _, val := range vals {
+			if val == "autogenerated" {
+				path, err := bsp.getAutogeneratedLinkerScriptPath()
+				if err != nil {
+					return nil, util.PreNewtError(err,
+						"Could not resolve autogenerated linker script path for target \"%s\"",
+						bsp.yov.Pkg.Name())
+				}
+				paths = append(paths, path)
+				continue
+			}
+
 			path, err := proj.ResolvePath(ypkg.Repo().Path(), val)
 			if err != nil {
 				return nil, util.PreNewtError(err,
@@ -226,7 +255,6 @@ func NewBspPackage(lpkg *LocalPackage, yov *BspYCfgOverride) (*BspPackage, error
 	lpkg.Load()
 	bsp.LocalPackage = lpkg
 	bsp.BspV = ycfg.NewYCfg(bsp.BspYamlPath())
-
 	err := bsp.Reload(nil)
 
 	return bsp, err