Restrict genrules to disallow directories as input

While Bazel genrules will allow genrules to accept a directory as input,
the results can be unexpected to a user as changes to the contents of
the directory may not trigger a rebuild as expected. Restricting this
in Soong ensures that converted targets will behave as expected.

Test: CI
Change-Id: I8616f58d1df267005e6c0ca3f4730d06de52c0d9
diff --git a/android/variable.go b/android/variable.go
index 627d9bd..68f19b9 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -421,9 +421,10 @@
 
 	ShippingApiLevel *string `json:",omitempty"`
 
-	BuildBrokenEnforceSyspropOwner     bool `json:",omitempty"`
-	BuildBrokenTrebleSyspropNeverallow bool `json:",omitempty"`
-	BuildBrokenVendorPropertyNamespace bool `json:",omitempty"`
+	BuildBrokenEnforceSyspropOwner     bool     `json:",omitempty"`
+	BuildBrokenTrebleSyspropNeverallow bool     `json:",omitempty"`
+	BuildBrokenVendorPropertyNamespace bool     `json:",omitempty"`
+	BuildBrokenInputDirModules         []string `json:",omitempty"`
 
 	BuildDebugfsRestrictionsEnabled bool `json:",omitempty"`