rust: Mutate prebuilt modules dylib/rlib

This change makes it possible to use a single module to provide both
dylib and rlib varieties of a library. This allows the use of libstd and
libtest from a rustlibs property, allowing linkage type to change
for different variants.

Bug: 159718669
Test: cd external crates; mma; m crosvm.experimental
Change-Id: I477c4d2faec63703fdc6dd42ba020747d6a50714

rust/rust.go

@@ -440,6 +440,9 @@ func (mod *Module) HasStaticVariant() bool {
 
 func (mod *Module) CoverageFiles() android.Paths {
 	if mod.compiler != nil {
+		if !mod.compiler.nativeCoverage() {
+			return android.Paths{}
+		}
 		if library, ok := mod.compiler.(*libraryDecorator); ok {
 			if library.coverageFile != nil {
 				return android.Paths{library.coverageFile}