Refactor CC to prep for Rust sanitizable modules.

Adds a PlatformSanitizable interface which both CC and Rust can
implement so that the sanitizer mutators in CC can sanitize Rust
shared/static libraries appropriately.

Bug: 147140513
Test: m nothing
Change-Id: Ib31103b6c4902a4d5df2565c0d7c981298d100a3
diff --git a/rust/binary.go b/rust/binary.go
index c2d97f3..ca07d07 100644
--- a/rust/binary.go
+++ b/rust/binary.go
@@ -164,3 +164,7 @@
 	}
 	return binary.baseCompiler.stdLinkage(ctx)
 }
+
+func (binary *binaryDecorator) isDependencyRoot() bool {
+	return true
+}