Support tailoring clang --target flag based on min sdk version.

Bug: 215748260
Test: Tested using aquery to verify the --target flag; add added unit

Change-Id: Ifb13509db7d1e110316aa44d55ec9cccaa4b83d1
diff --git a/bp2build/conversion.go b/bp2build/conversion.go
index 3ab846b..91e614d 100644
--- a/bp2build/conversion.go
+++ b/bp2build/conversion.go
@@ -36,6 +36,7 @@
 	}
 	files = append(files, newFile("api_levels", GeneratedBuildFileName, `exports_files(["api_levels.json"])`))
 	files = append(files, newFile("api_levels", "api_levels.json", string(apiLevelsContent)))
+	files = append(files, newFile("api_levels", "api_levels.bzl", android.StarlarkApiLevelConfigs(cfg)))
 
 	return files
 }