Update musl bindgen clang lib directory

Musl libclang.so is in musl/lib, not musl/lib64.

Bug: 216192129
Test: m USE_HOST_MUSL=true host-native -k
Change-Id: Id12630d5c0f51d85278f8562b3d988458a56021a

rust/bindgen.go

@@ -51,7 +51,7 @@ var (
 	})
 	_ = pctx.VariableFunc("bindgenClangLibdir", func(ctx android.PackageVarContext) string {
 		if ctx.Config().UseHostMusl() {
-			return "musl/lib64/"
+			return "musl/lib/"
 		} else {
 			return "lib64/"
 		}