Allow //external/bazel-skylib to use existing BUILD files

Bug: 190605804
Test: bp2build-incremental
Change-Id: Ida765465532c0e98d035eef4c703d13fbf554538
diff --git a/android/bazel.go b/android/bazel.go
index 6942d57..8c86a95 100644
--- a/android/bazel.go
+++ b/android/bazel.go
@@ -149,6 +149,7 @@
 		// external/bazelbuild-rules_android/... is needed by mixed builds, otherwise mixed builds analysis fails
 		// e.g. ERROR: Analysis of target '@soong_injection//mixed_builds:buildroot' failed
 		"external/bazelbuild-rules_android":/* recursive = */ true,
+		"external/bazel-skylib":/* recursive = */ true,
 
 		"prebuilts/jdk":/* recursive = */ true,
 		"prebuilts/sdk":/* recursive = */ false,