Sandbox genrule tools

Copy tools used by genrules into the sandbox directory.  This
ensures correct dependencies on all files used by tools, and
is one step closer to enabling genrules inside unselected
namespaces.

Bug: 124313442
Test: genrule_test.go
Test: rule_builder_test.go
Test: m checkbuild
Change-Id: I38393900677c5dbe8e72fe06a7dd7d71f3c09f82
diff --git a/android/module.go b/android/module.go
index 0bd64ed..2bcc7a8 100644
--- a/android/module.go
+++ b/android/module.go
@@ -2732,6 +2732,7 @@
 // Modules can implement HostToolProvider and return a valid OptionalPath from HostToolPath() to
 // specify that they can be used as a tool by a genrule module.
 type HostToolProvider interface {
+	Module
 	// HostToolPath returns the path to the host tool for the module if it is one, or an invalid
 	// OptionalPath.
 	HostToolPath() OptionalPath