configure: MSVC 2015 finally supports C++11 thread-safe statics

Change-Id: If0e644298c655487cf97609a66ee37c5b4bd70ae

configure.ac

@@ -5872,7 +5872,14 @@ if test "$GCC" = "yes"; then
         AC_MSG_RESULT([broken (i.e., no)])
     fi
 else
-    AC_MSG_RESULT([unknown (assuming no)])
+    # MSVC has sprouted C++11 thread-safe statics in 2015
+    # http://blogs.msdn.com/b/vcblog/archive/2015/06/19/c-11-14-17-features-in-vs-2015-rtm.aspx
+    if test "$COM" = "MSC" -a "$VCVER" -ge "140"; then
+        AC_DEFINE(HAVE_THREADSAFE_STATICS)
+        AC_MSG_RESULT([yes])
+    else
+        AC_MSG_RESULT([no])
+    fi
 fi
 AC_SUBST(HAVE_THREADSAFE_STATICS)