Work around overly strict restrict checks by MSVC.
Apparently MSVC requires a * before a restrict in a variable
declaration, even if the adorned type already is a pointer, just via
typedef.
As reported by buildfarm animal woodlouse.
Author: Andres Freund
Discussion: https://postgr.es/m/
20171012001320.4putagiruuehtvb6@alap3.anarazel.de