rust: Emit toc files for cdylibs

Write toc files that list the exported symbols so dependents are
only rebuilt if the exported symbols change.

This exports the CC function TransformSharedObjectToToc, and also
removes an unused arg from its signature.

Bug: 178185435
Test: New Soong test passes.
Test: m <toc file path>
Change-Id: I7ab69bf7e7f32f25eb4c7ca9d18d877dac1511db
diff --git a/rust/builder.go b/rust/builder.go
index f79cf9b..6f20347 100644
--- a/rust/builder.go
+++ b/rust/builder.go
@@ -185,7 +185,7 @@
 }
 
 func transformSrctoCrate(ctx ModuleContext, main android.Path, deps PathDeps, flags Flags,
-	outputFile android.WritablePath, crate_type string) buildOutput {
+	outputFile android.WritablePath, crateType string) buildOutput {
 
 	var inputs android.Paths
 	var implicits android.Paths
@@ -204,7 +204,7 @@
 	// Collect rustc flags
 	rustcFlags = append(rustcFlags, flags.GlobalRustFlags...)
 	rustcFlags = append(rustcFlags, flags.RustFlags...)
-	rustcFlags = append(rustcFlags, "--crate-type="+crate_type)
+	rustcFlags = append(rustcFlags, "--crate-type="+crateType)
 	if crateName != "" {
 		rustcFlags = append(rustcFlags, "--crate-name="+crateName)
 	}