Disable unwanted C++ definitions for MSVC.

MSVC does not set __cplusplus to the latest standard and also it does not like redefining some keywords.

src/hb.hh

diff --git a/src/hb.hh b/src/hb.hh
index 5b66ba8..67f09b9 100644
--- a/src/hb.hh
+++ b/src/hb.hh
@@ -214,7 +214,7 @@
  * Compiler attributes
  */
 
-#if __cplusplus < 201103L
+#if __cplusplus < 201103L && !defined(_MSC_VER)
 
 #ifndef nullptr
 #define nullptr NULL