win: optionally allow node.exe/iojs.exe to be renamed

On Windows, when node or io.js attempts to dynamically load a compiled
addon, the compiled addon tries to load node.exe or iojs.exe again -
depending on which import library the module used when it was linked.
This causes many compiled addons to break when node.exe or iojs.exe are
renamed, because when the binary has been renamed the addon DLL can't
find the (right) .exe file to load its imports from.

This patch gives compiled addon developers an option to overcome this
restriction by compiling a delay-load hook into their binary. The
delay-load hook ensures that whenever a module tries to load imports
from node.exe/iojs.exe, it'll just look at the process image, thereby
making the addon work regardless of what name the node/iojs binary has.

To enable this feature, the addon developer must set the
'win_delay_load_hook' option to 'true' in their binding.gyp file, like
this:

```
{
  'targets': [
    {
      'target_name': 'ernie',
      'win_delay_load_hook': 'true',
      ...
```

Bug: nodejs/node#751
Bug: nodejs/node#965

addon.gypi

@@ -1,7 +1,9 @@
 {
   'target_defaults': {
     'type': 'loadable_module',
+    'win_delay_load_hook': 'false',
     'product_prefix': '',
+
     'include_dirs': [
       '<(node_root_dir)/src',
       '<(node_root_dir)/deps/uv/include',
@@ -13,11 +15,34 @@
         'product_extension': 'node',
         'defines': [ 'BUILDING_NODE_EXTENSION' ],
       }],
+
       ['_type=="static_library"', {
         # set to `1` to *disable* the -T thin archive 'ld' flag.
         # older linkers don't support this flag.
         'standalone_static_library': '<(standalone_static_library)'
       }],
+
+      ['_win_delay_load_hook=="true"', {
+        # If the addon specifies `'win_delay_load_hook': 'true'` in its
+        # binding.gyp, link a delay-load hook into the DLL. This hook ensures
+        # that the addon will work regardless of whether the node/iojs binary
+        # is named node.exe, iojs.exe, or something else.
+        'conditions': [
+          [ 'OS=="win"', {
+            'sources': [
+              'src/win_delay_load_hook.c',
+            ],
+            'msvs_settings': {
+              'VCLinkerTool': {
+                'DelayLoadDLLs': [ 'iojs.exe', 'node.exe' ],
+                # Don't print a linker warning when no imports from either .exe
+                # are used.
+                'AdditionalOptions': [ '/ignore:4199' ],
+              },
+            },
+          }],
+        ],
+      }],
     ],
 
     'conditions': [

src/win_delay_load_hook.c

@@ -0,0 +1,32 @@
+/*
+ * When this file is linked to a DLL, it sets up a delay-load hook that
+ * intervenes when the DLL is trying to load 'node.exe' or 'iojs.exe'
+ * dynamically. Instead of trying to locate the .exe file it'll just return
+ * a handle to the process image.
+ *
+ * This allows compiled addons to work when node.exe or iojs.exe is renamed.
+ */
+
+#ifdef _MSC_VER
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#include <delayimp.h>
+#include <string.h>
+
+static FARPROC WINAPI load_exe_hook(unsigned int event, DelayLoadInfo* info) {
+  if (event != dliNotePreLoadLibrary)
+    return NULL;
+
+  if (_stricmp(info->szDll, "iojs.exe") != 0 &&
+      _stricmp(info->szDll, "node.exe") != 0)
+    return NULL;
+
+  HMODULE m = GetModuleHandle(NULL);
+  return (FARPROC) m;
+}
+
+PfnDliHook __pfnDliNotifyHook2 = load_exe_hook;
+
+#endif