Temporary attempt at a workaround for further MSVC restrict build failures.

It appears some versions of msvc use __declspec(restrict) in stdlib.h
and subsidiary headers. Including those after defining 'restrict' to
'__restrict' doesn't work.  Try to get the buildfarm green to see
whether there's further problems, by including stdlib.h just before
said define.

src/include/pg_config.h.win32

@@ -687,6 +687,11 @@
 /* Visual Studio 2008 and upwards */
 #if (_MSC_VER >= 1500)
 /* works for C and C++ in msvc */
+/*
+ * Temporary attempt at a workaround for stdlib.h's use of
+ * declspec(restrict), conflicting with below define.
+ */
+#include <stdlib.h>
 #define restrict __restrict
 #else
 #define restrict