Add a common interface for cc linkable libraries.

Adds an interface, CcLinkableInterface, for cc linkable dependencies
which come from other toolchains such as Rust.

Bug: 140726209
Test: Soong tests pass, rust modules still compile.
Change-Id: I7378a46fad94fd0b735746aaf4e265fd2c2c04d8
diff --git a/Android.bp b/Android.bp
index 714ce37..05972fd 100644
--- a/Android.bp
+++ b/Android.bp
@@ -157,6 +157,7 @@
         "cc/check.go",
         "cc/coverage.go",
         "cc/gen.go",
+        "cc/linkable.go",
         "cc/lto.go",
         "cc/makevars.go",
         "cc/pgo.go",