Delay dependency errors to ninja time for unbundled builds

Unbundled builds may use a subset of the tree, which can bring in unused
modules but not their dependencies.  Delay handling of dependency errors
for unbundled builds to ninja time, which will prevent errors if only
modules with satisified dependencies are built.

Change-Id: Ib93bae93fcfa0b55df500a30d8e35231ffb0987c
diff --git a/common/config.go b/common/config.go
index 971c4c1..74e0660 100644
--- a/common/config.go
+++ b/common/config.go
@@ -22,8 +22,12 @@
 	"runtime"
 	"strings"
 	"sync"
+
+	"github.com/google/blueprint/proptools"
 )
 
+var Bool = proptools.Bool
+
 // The configuration file name
 const configFileName = "soong.config"
 const productVariablesFileName = "soong.variables"
@@ -287,3 +291,7 @@
 func (c *config) DefaultAppCertificate(ctx PathContext) SourcePath {
 	return c.DefaultAppCertificateDir(ctx).Join(ctx, "testkey")
 }
+
+func (c *config) AllowMissingDependencies() bool {
+	return Bool(c.ProductVariables.Unbundled_build)
+}