update llama.cpp submodule to `4bd0f93` (#3627)

llm/llama.cpp

@@ -1 +1 @@
-Subproject commit 1b67731e184e27a465b8c5476061294a4af668ea
+Subproject commit 4bd0f93e4ab4fe6682e7d0241c1bdec1397e954a