Add a test for b builds with --

Using -- to indicate the end of arguments has caused issues multiple
times in the past.

Test: ./build/make/tests/roboleaf_tests.sh
Change-Id: I4aef2f1672b917587dd9a2dbe15934db0b0ae0cd
diff --git a/tests/b_tests.sh b/tests/b_tests.sh
index 13f156d..491d762 100755
--- a/tests/b_tests.sh
+++ b/tests/b_tests.sh
@@ -24,6 +24,7 @@
 test_target=//build/bazel/scripts/difftool:difftool
 
 b build "$test_target"
+b build -- "$test_target"
 b build "$test_target" --run-soong-tests
 b build --run-soong-tests "$test_target"
 b --run-soong-tests build "$test_target"