Close DynamicLibraries in reverse order they were opened.

[marsupial]

Summary

Matches C++ destruction ordering better and fixes possible problems of loaded libraries having inter-dependencies.

[efriedma]

Needs a testcase, I think. Otherwise, looks fine.

[marsupial]

Add test case.

[efriedma]

LGTM.

lib/Support/DynamicLibrary.cpp

 //===-- DynamicLibrary.cpp - Runtime link/load libraries --------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file implements the operating system DynamicLibrary concept.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/DynamicLibrary.h"
 #include "llvm-c/Support.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/iterator_range.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Mutex.h"
 #include <cstdio>
 #include <cstring>
 #include <vector>
 

lib/Support/Unix/DynamicLibrary.inc

 // This file provides the UNIX specific implementation of DynamicLibrary.
 //
 //===----------------------------------------------------------------------===//
 
 #if defined(HAVE_DLFCN_H) && defined(HAVE_DLOPEN)
 #include <dlfcn.h>
 
 DynamicLibrary::HandleSet::~HandleSet() {
-  for (void *Handle : Handles)
+  // Close the libraries in reverse order.
+  for (void *Handle : llvm::reverse_range(Handles))
     ::dlclose(Handle);
   if (Process)
     ::dlclose(Process);
 }
 
 void *DynamicLibrary::HandleSet::DLOpen(const char *File, std::string *Err) {
   void *Handle = ::dlopen(File, RTLD_LAZY|RTLD_GLOBAL);
   if (!Handle) {

lib/Support/Windows/DynamicLibrary.inc

 
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only Win32 specific code
 //===          and must not be UNIX code.
 //===----------------------------------------------------------------------===//
 
 
 DynamicLibrary::HandleSet::~HandleSet() {
-  for (void *Handle : Handles)
+  for (void *Handle : llvm::reverse_range(Handles))
     FreeLibrary(HMODULE(Handle));
 
   // 'Process' should not be released on Windows.
   assert((!Process || Process==this) && "Bad Handle");
 }
 
 void *DynamicLibrary::HandleSet::DLOpen(const char *File, std::string *Err) {
   // Create the instance and return it to be the *Process* handle