update llama.cpp submodule to `1b67731` (#3561)

llm/llama.cpp

@@ -1 +1 @@
-Subproject commit 37e7854c104301c5b5323ccc40e07699f3a62c3e
+Subproject commit 1b67731e184e27a465b8c5476061294a4af668ea