add description

Author: PeterChou1

llvm/docs/CommandGuide/llvm-mustachespec.rst

@@ -1,5 +1,5 @@
-llvm-mustachespec
-=================
+llvm-mustachespec - LLVM tool to test Mustache Compliance Library
+=================================================================
 
 llvm-mustachespec test the mustache spec conformance of the LLVM
 mustache library. The spec can be found here https://github.com/mustache/spec

llvm/test/lit.cfg.py

@@ -233,7 +233,6 @@ def get_asan_rtlib():
         "llvm-c-test",
         "llvm-cxxfilt",
         "llvm-xray",
-        "llvm-mustachespec"
         "yaml2obj",
         "obj2yaml",
         "yaml-bench",