[fusl] Add llvm's lit tool to third_party

third_party/lit/tests/Inputs/discovery/lit.cfg

Index: third_party/lit/tests/Inputs/discovery/lit.cfg
diff --git a/third_party/lit/tests/Inputs/discovery/lit.cfg b/third_party/lit/tests/Inputs/discovery/lit.cfg
new file mode 100644
index 0000000000000000000000000000000000000000..c48ca0bc036517549de01231ee2172b035fc5647
--- /dev/null
+++ b/third_party/lit/tests/Inputs/discovery/lit.cfg
@@ -0,0 +1,14 @@
+import lit.formats
+config.name = 'top-level-suite'
+config.suffixes = ['.txt']
+config.test_format = lit.formats.ShTest()
+
+# We intentionally don't set the source root or exec root directories here,
+# because this suite gets reused for testing the exec root behavior (in
+# ../exec-discovery).
+#
+#config.test_source_root = None
+#config.test_exec_root = None
+
+# Check that arbitrary config values are copied (tested by subdir/lit.local.cfg).
+config.an_extra_variable = False