Add missing dependency in create_mock_soong

This change adds missing dependency of Soong modules as symlink
directory in create_mock_soong so that a correct ninja graph can be
created when invoking androidmk_test.sh.

Test: build/soong/test/run_integration_tests.sh
Bug: 283905797
Change-Id: I7dff0094fdc23b7c438c917dbc00a5143a4dc5ae
diff --git a/tests/lib.sh b/tests/lib.sh
index 715eac1..7f3970e 100644
--- a/tests/lib.sh
+++ b/tests/lib.sh
@@ -99,6 +99,7 @@
   symlink_directory external/python
   symlink_directory external/sqlite
   symlink_directory external/spdx-tools
+  symlink_directory libcore
 
   touch "$MOCK_TOP/Android.bp"
 }