Add IAT based hooking to allow hooking 64bit opengl32.dll

* Needs vigorous testing in as many situations as I can think of, not least
  32bit, 64bit, D3D11, D3D9, OpenGL, managed apps, different windows SDKs,
  delay loading dlls (not sure if these will work), statically linked libs,
  LoadLibrary + GetProcAddress
* Credit goes to jslutter for originally bringing it to my attention &
  suggesting it.
* References:
  http://msdn.microsoft.com/en-us/magazine/bb985992.aspx
  http://msdn.microsoft.com/en-us/magazine/cc301808.aspx
  http://www.codeproject.com/Articles/6265/Process-wide-API-spying-an-ultimate-hack

renderdoc/os/win32/win32_process.cpp

@@ -292,6 +292,7 @@ uint32_t Process::InjectIntoProcess(uint32_t pid, const wchar_t *logfile, const
 	}
 #endif
 
+#if USE_MHOOK
 	// misc
 	InjectDLL(hProcess, L"kernel32.dll");
 
@@ -303,6 +304,7 @@ uint32_t Process::InjectIntoProcess(uint32_t pid, const wchar_t *logfile, const
 	// OpenGL
 	InjectDLL(hProcess, L"opengl32.dll");
 	InjectDLL(hProcess, L"gdi32.dll");
+#endif
 
 	InjectDLL(hProcess, renderdocPath);