[dfsan] Turn off THP at dfsan_flush

[stephan.yichao.zhao]

Summary

https://reviews.llvm.org/D89662 turned this off at dfsan_init.
dfsan_flush also needs to turn it off.
W/o this a program using dfsan_flush may get more and more memory usage after hours.

[morehouse]

LGTM

compiler-rt/lib/dfsan/dfsan.cpp

if (internal_strcmp(flags().dump_labels_at_exit, "") != 0) {
     Report("INFO: DataFlowSanitizer: dumping labels to %s\n",
            flags().dump_labels_at_exit);
     dfsan_dump_labels(fd);
     CloseFile(fd);
   }
 }
 
 extern "C" void dfsan_flush() {
-  if (!MmapFixedNoReserve(ShadowAddr(), UnusedAddr() - ShadowAddr()))
+  if (!MmapFixedSuperNoReserve(ShadowAddr(), UnusedAddr() - ShadowAddr()))
     Die();
 }
 
 static void dfsan_init(int argc, char **argv, char **envp) {
   InitializeFlags();
 
   ::InitializePlatformEarly();
 
-  if (!MmapFixedSuperNoReserve(ShadowAddr(), UnusedAddr() - ShadowAddr()))
-    Die();
+  dfsan_flush();
   if (common_flags()->use_madv_dontdump)
     DontDumpShadowMemory(ShadowAddr(), UnusedAddr() - ShadowAddr());
 
   // Protect the region of memory we don't use, to preserve the one-to-one
   // mapping from application to shadow memory. But if ASLR is disabled, Linux
   // will load our executable in the middle of our unused region. This mostly
   // works so long as the program doesn't use too much memory. We support this
   // case by disabling memory protection when ASLR is disabled.