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/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(Handles))
     ::dlclose(Handle);
   if (Process)
     ::dlclose(Process);
 
   // llvm_shutdown called, Return to default
   DynamicLibrary::SearchOrder = DynamicLibrary::SO_Linker;
 }
 

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(Handles))
     FreeLibrary(HMODULE(Handle));
 
   // 'Process' should not be released on Windows.
   assert((!Process || Process==this) && "Bad Handle");
   // llvm_shutdown called, Return to default
   DynamicLibrary::SearchOrder = DynamicLibrary::SO_Linker;
 }