Temporarily disable PTH stat caching as it appears to be failing on some machines.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@64354 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Lex/PTHLexer.cpp

@@ -825,5 +825,6 @@ public:
 };
 
 StatSysCallCache *PTHManager::createStatCache() {
-  return new PTHStatCache(*((PTHFileLookup*) FileLookup));
+  return 0;
+//  return new PTHStatCache(*((PTHFileLookup*) FileLookup));
 }