DynamicLoader: support loading sibling libraries on Windows

DynamicLoader.cxx

@@ -217,9 +217,15 @@ namespace KWSYS_NAMESPACE {
 DynamicLoader::LibraryHandle DynamicLoader::OpenLibrary(
   const std::string& libname, int flags)
 {
-  CHECK_OPEN_FLAGS(flags, 0, NULL);
+  CHECK_OPEN_FLAGS(flags, SearchBesideLibrary, NULL);
+
+  DWORD llFlags = 0;
+  if (flags & SearchBesideLibrary) {
+    llFlags |= LOAD_WITH_ALTERED_SEARCH_PATH;
+  }
 
-  return LoadLibraryW(Encoding::ToWindowsExtendedPath(libname).c_str());
+  return LoadLibraryExW(Encoding::ToWindowsExtendedPath(libname).c_str(), NULL,
+                        llFlags);
 }
 
 int DynamicLoader::CloseLibrary(DynamicLoader::LibraryHandle lib)

DynamicLoader.hxx.in

@@ -68,7 +68,12 @@ public:
 
   enum OpenFlags
   {
-    AllOpenFlags = 0
+    // Search for dependent libraries beside the library being loaded.
+    //
+    // This is currently only supported on Windows.
+    SearchBesideLibrary = 0x00000001,
+
+    AllOpenFlags = SearchBesideLibrary
   };
 
   /** Load a dynamic library into the current process.