bp2build BUILD files for build/bazel/examples/apex.

The previous build/bazel recursive glob is too aggressive. Not all
directories should be ignored by bp2build.

Test: bp2build-incremental builds //bionic/... and everything it depends on in //build/bazel/...
Bug: 193658718
Change-Id: Icb48fd687f0fe6be144caa5b8c9a4f01d15b6c20
diff --git a/android/bazel.go b/android/bazel.go
index d40e650..f72fd40 100644
--- a/android/bazel.go
+++ b/android/bazel.go
@@ -127,11 +127,22 @@
 
 var (
 	// Keep any existing BUILD files (and do not generate new BUILD files) for these directories
+	// in the synthetic Bazel workspace.
 	bp2buildKeepExistingBuildFile = map[string]bool{
 		// This is actually build/bazel/build.BAZEL symlinked to ./BUILD
 		".":/*recursive = */ false,
 
-		"build/bazel":/* recursive = */ true,
+		// build/bazel/examples/apex/... BUILD files should be generated, so
+		// build/bazel is not recursive. Instead list each subdirectory under
+		// build/bazel explicitly.
+		"build/bazel":/* recursive = */ false,
+		"build/bazel/examples/android_app":/* recursive = */ true,
+		"build/bazel/bazel_skylib":/* recursive = */ true,
+		"build/bazel/rules":/* recursive = */ true,
+		"build/bazel/rules_cc":/* recursive = */ true,
+		"build/bazel/tests":/* recursive = */ true,
+		"build/bazel/platforms":/* recursive = */ true,
+		"build/bazel/product_variables":/* recursive = */ true,
 		"build/pesto":/* recursive = */ true,
 
 		// external/bazelbuild-rules_android/... is needed by mixed builds, otherwise mixed builds analysis fails